Knowing Riot, this will create more issues rather than resolve them. You'll end up with champions that are extremely strong early (and require armor to counter in your runes, heavily so), say Lee Sin JG, Zed mid, Talon mid, Darius top, etc. and you can't counter them in the slightest. There will be no variation in early build that ultimately determines which build is the most efficient at countering the, and while individuality might be initially better expressed through the new runes system, it will likewise deteriorate into 'Which is the only viable choice for me'.
For example, not taking undying grasp on a tank will leave you at a startling and massive disadvantage, if say you were to opt for the summoner spell change, you'd be losing about 500 HP worth of stats by 20-25 minutes.
Not taking Gathering storm on a non-tank carry will result in massive deficits, more particularly for AD champions than AP champions, the later the game goes it becomes radically efficient. Whereas more AP is never bad, it's not that hard to constantly gather more of it, to the point that it becomes ridiculous. AD on the other hand, in particular for bruisers, is reasonably difficult to come into while maintaining a sizably sturdy build. Case and point, taking Undying Grasp on say Darius, will result in massive health gains (300 health would be reasonably obtainable by 20 minutes even if struggling to constantly proc it), and then grabbing Gathering Storm, if the game goes on late enough, you'd be looking at a thousand or more free HP in stats, in addition to a 100 or more AD stacked on top of that.
If you're in an extremely high elo, in which matches are consistently and commonly decided AND ended before the 20 minute mark, than the majority of choices are bad for you. You'll likely end up taking whatever keystone in particular is best for you (new thunderlords, new fervor, undying grasp, or lethal tempo), and then slotting in the inspiration tree for a free 350g worth of boots and a 600g stopwatch, that's a free 950g worth of items before 10 minutes. The boots are worth 300g + upgrade for 50g cheaper, which is why they are valued at 350g.
That may not be your main items, but that's a lot of freed up tertiary spending that can instead be redirected into your primary items, especially for that early into the game. You can use stopwatch to dodge a tower shot during a dive, survive a dive, outlast ignite, etc. it's essentially a one-time use Zhonya's hourglass, and then can be invested and upgraded into a Zhonya's, Stoneplate, or GA. And boots, are boots. Essentially, instead of buying boots, you're grabbing an extra dagger as ADC. Instead of dying to the minions after grabbing a kill, you're using stopwatch to survive.
On AP champs into harder matchups, this build is more or less required, the stopwatch makes Zhonya's obtainable quicker, and allows you to survive a Zed's deathmark, etc. It makes Zhonya's Hourglass 2300g instead of 2900g. 70 AP, 45 armor, 10% cdr, and the active, all for 2300g if you take this rune.
Nothing else will be viable in higher elos by comparison.
People think there will be varying setups, and for the smaller choices (which secondary tree to take) there might be, for some characters or roles. But, that's completely dependent on elo.
Would an ADC player rather have unlimited stacking AD, or the occasional attack that hits for 100 damage + like 20% of your AD. Would they rather have 8 free AD at 10 minutes, 24 AD at 20 minutes, etc. or have the occasional ward that stays in whatever bush they were in, until someone facechecks it, or after getting 5 unique takedowns, get a total of 15% spellvamp, only 33% effective on their aoe abilities. They also have the option of an 18-35 HP heal with a 0.2 AD ratio, on a 20 second CD.
There are SOME options that are truly interesting or unique, but for the most part, it feels like there will be comparable and diminutive player choice involved. If you take an off-meta build you're going to be severely punished for it, as your opponent won't have, and a lot of the advantages of these new rune-builds are so overwhelmingly efficient for champs that can abuse and use them, and not usable by others.
Assuming for one option, 300 minions or monsters die near you, you get a 7.5% max health increase. Wow, how massive. For the tank that has 4,000 HP, that's a 300 HP INCREASE!!!!!!!!!!!! But, completely useless on Junglers or non-tank stacking characters, pretty much until the character has maxed out their HP items.
That's 800g worth of stats (not necessarily worth it by comparison of similar options; i.e. nullifying orb to survive a magic attack, ultimate hat for quick regen of your ultimate, 10% free cdr, gathering storm's massive efficiency the later the game goes if on a target that can use it (i.e. red Kayn for the massively increased damage and therefore self healing, Darius for similar reasons). It just requires such a situational rationale 'be near 300 minion and or monster deaths' to get a 7.5% max HP increase, now while it is a passive effect, and it's combination with Undying Grasp on certain champs (looking at you Sion) would be rather disgusting, outside of niche specialties, this rune will never be the most efficient or even potentially viable choice for the majority of characters or builds. Playing as a jungler in particular, you have to be in XP range (and therefore griefing your laner) to get any sort of real benefit from this, as you'll never kill or be near enough dead monsters or creeps to efficiently stack this up.
It's really going to come down to "What kind of champ am I playing?" and "Here is the only efficient or viable build", not taking Ravenous Hunter on Akali will cripple you by comparison of those Akali players who DO take it. Not taking Electrocute on ANY Assassin will gimp you. Not taking Lethal Temp on Kog'Maw, and assuming no serious changes are made to Ardent Censer, that too on a Janna or Lulu sitting on him, you'll be completely and overwhelmingly pathetic by comparison of one who does. Having a Blitzcrank support will be completely non-competitive compared to say Lulu support for Kog'Maw, taking the speed up, or Press the Attack, will be extremely bad by comparison of Lethal Tempo (it gives massive free attackspeed, and allows you to exceed the attackspeed cap).
Say 2.5 attacks per second Kog'Maw, 4 x 2.5 is 10 attacks, 9 + 18 + 27 + 36 + 45 + 54 + 63 + 72 + 81 + 90 = 495
Now say you were to hit 4.5 attacks per second instead, which is quite possible, 4.5 x 4 = 18 attacks in the same time span, 8 more attacks.
Assuming each attack has 100 on hit damage, quite reasonable given his W + any standardized build on him, that's 800 damage, or 305 more damage than the alternative. In reality, it's actually even MORE efficient than that, as his W + on hit effects are probably closer to 300-400 damage an attack, rather than 100. Assuming you were even at 250 damage an attack, with only a 3.3 attackspeed vs 2.5, 13.2 attacks (roughly 3 more attacks in the same timespan), that's 750 damage. It is a completely unviable option compared to Lethal Tempo, and never can be comparable.
Taking Grasp of the Undying as jungler get you reported for trolling as well, given it's only efficiency is through repeated stacking against enemy champions, and the odds of that are extremely unlikely of ever occurring enough for it to be even worth more than 100-200g worth of bonus HP by 20 minutes. B/c the simple lack of efficiency in the choice is so egregious that you might as well be tossing out hundreds of gold, and choosing to put your team into a situation in which they are unfairly disadvantaged. Is this right? Probably not, but they might as well be taking Stoneborn pact on Sivir for all the worth this Keystone would be worth to the jungler, and doing so intentionally.
Comparing Lethal Tempo to Fleet Footwork, outside of Jhin who has no viable alternatives in the tree (and will likely venture off into the Sorcery Tree for comet), what reasonable person would take Fleet Footwork over Lethal Tempo on any on-hit reliant ADC, or over Press the Attack on any AD-focused ADC (Xayah, Caitlyn, Vayne would be examples of scaling reasonable well with this choice over Lethal Tempo, and by far the Footwork is comparably useless).
At the end of the day, we're exchanging our current runes and masteries system, for something that looks a little different, but will be no different in regards to the 'making or breaking' of characters based primarily on base-builds. Some players will still have bad builds, and the difference in a good build and a bad build will be so staggering that the 'bad' build won't be competitive when put on players of equal skill. It'll change the meta, for a time, but it'll simply reform as a new meta, which will be comparable in rigidity as our current one (How many times did they say Ardent Censer at worlds?).
This isn't really a rant, I'm just trying to clarify that there won't be any real and legitimate variety present. It's no different than current, sure you can choose to take Undying Grasp on an ADC, just be prepared to be at an inherent and massive disadvantage. Taking full HP runes on an ADC, you can do that, but when compared to one who took the 'proper and meta' choice, you will be unable to compete, not in an even skill matchup at least. Instead of 'full hp runes', it will simply be choosing to take Overgrowth and Perseverance over Gathering Storm and Ultimate Hat on say Ashe.
Once the final numbers are in, and based on build, it'll become quite clear which is better, Lethal Tempo or Press the Attack (as Footwork is not in the running at all) for Ashe, and choosing the non-optimal choice is always the incorrect option.
If the meta is shifting to late game, then taking anything but late game scaling runes is bad.
If the meta is shifting to early game, then taking anything but short-term benefit runes is bad.
Not taking Electrocute on Zed is going to be a massive handicap; no other option is reasonably viable for him.
I'm writing this extremely tired, so expect many mistakes that I didn't catch. Just sound it out, you'll probably understand what I'm talking about