I think the issue I have with it currently is that the runes you get are too randomized. There are a ton of runes that are useless, if not straight up counterproductive on certain champions. This makes the rune feel clunky and poorly conceived because there are times when it's kind've good (namely when you pray to rnjesus and roll that natural D20) and times (the majority) where it feels more like a burden than anything.
If I had to name a suggestion, it would be to add some measure of manipulation to the rune so that you could customize the runes it is more likely to cycle through, with some drawbacks.
Like, for example: Imagine upon selecting the rune, you're asked to choose 3 other unique runes from any combination of rune trees. So for example: You want to play volibear, who benefits from being able to rush down and so you take predator. You want tankiness on demand in certain scenarios where your team needs you to soak damage for the backline, so you take aftershock. You need 1v1 potential versus the enemy jungler, so you take conqueror. These runes will roll amongst each other every 15 seconds, with this timer resetting while in combat. This gives you time to see the rune you want and plan out how you'll choose to fight, being able to stall the change by fighting minions or clearing jungle camps. When runes are on cooldown, they'll be disqualified from the rolling process until they aren't, allowing you to manipulate what you get, within reason. So when you've used predator and aftershock, you're guaranteed to get conqueror and the like.
Being able to limit the runes you get offers you the ability to choose your synergy, which promotes gameplay decisions and choice, which I think is important. Obviously checks and balances need to be in place so you aren't constantly rnj-activating arcane comet 5 times back to back and winning your lane through bs. So using their cooldowns to decide when they are eligible for being rolled both offers more gameplay decisions for the player to predict and plan around, and also a balancing factor which keeps them from being abused.
Naturally, one of the potential issues that could come from this is that there are plenty of champions who benefit from having tons of options, so I could see this being abused to a degree. For example, the mid laner uses electrocute or comet to trade, then gets predator, clears their wave, and uses it to gank a lane. Or the support enchanter uses summon aery to help their carry via shields and heals, and stacks dark harvest alongside spellthief's on their enemy lane for a bit more scaling damage that might help in making picks. That said, I believe that, for one, having those options and being able to make those gameplay decisions would be a HUGE improvement and encourage higher level gameplay and micromanaging for the players, which could prevent it from being abused. Secondly, I also believe that the uptime of this rune could easily be tweaked to keep it from being too oppressive.
Sorry for the info dump, but this is all that I came up with while testing the rune. Any thoughts?