Karma's rework is making her slightly weaker as a mid laner, but much stronger as a junger then she was before. Karma can't be a Jungler because Magus is still terrible item on mages. Magus can't become a good item on Mages, because instead of buffing Magus to be good on Mages, Riot is trying to make Mages that work with Magus without making them into broken manaless midlaners with stronger power and utility.
CrazedPorcupine2 voteshonestly, all that needs to happen is the addition of mana leech on jungle camps. Like the old spirit stone. It doesn't work on plain minions, and is honestly only high enough to sustain jungle without blue buff. The biggest reason you don't see big mage junglers in the jungle anymore at the highest level, is because blue buff is not a guarantee to have.
NEW MAGUS: Still the smite upgrade + Fiendish Codex + fairy charm + 400 gold STATS: 80 AP +20% CDR Gain 5% of damage you deal to neutral monsters as mana (Smite upgrade of the smite you picked up)
BOOM Magus now introduces the return of Mage Junglers.
OR SPIRIT STONE: Amplifying tome + Fairy Charm + Rejuvination bead +105 gold = 900 gold 20 AP UNIQUE PASSIVE: 10% CDR +25% base mana regen +25% base health regen
MAGUS SMITE Upgrade+ Spirit Stone + 500 gold 80 AP 20% CDR Gain 4% of damage dealt to neutral monsters as hp and mana
TADAH!!! Mage junglers can actually exist.
Spirit stone not giving it's old unique passive until it becomes part of the jungle enchantment is to keep it from getting picked up mid lane, and it's not very efficient compared to Fiendish Codex since the only item that the new spirit stone builds into is the magus enchantment.
SlytherinUmbreon1 votesShe's probably still good in the toplane and support, just felt like pointing this part of it out.
Serevas1 votesYeah it seems like the attempt is to prevent a magus in the middle meta from occurring in addition to the smiting top laners, otherwise pretty soon we'd have all laners taking smite and building jungle items.
SlytherinUmbreon1 votesNot likely. For that to happen, Magus would have to be stronger then Morello and Athene's. Also, Mages (and assassins) don't benefit from any of the smites as much as Tanks do.
Cinderhulk + Skirmishers is being built on tanks because they've desperately needed a tank item that doesn't get shit on by 
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for a long time. Skirmisher's saber is the only source of Damage reduction in the game that isn't reduced by them. Added true damage, AoE, and % Health to that just made it something every tank in the game needed, but couldn't get from any other items.
Serevas1 votes
is another one, but I know where you're trying to get to with your point since top laners wouldn't be running Exhaust in place of Flash or TP, since that's massively inefficient.
If Magus had say....equal mana regen to Morellonomicon (That's the most logical buff to it from my perspective anyway, either that or mana leech.) I could see the use in going Magus instead of Morellonomicon. The reason is because if you're playing a bursty assassin, or even just a mage that builds Morellonomicon typically, the grievous wounds passive isn't really all that valuable when compared to having smite and the opponent smiting bonuses, especially if you consider that instead you could build a Magus Skirmisher's apply some true damage, and a damage reduction to your lane opponent. Taking smite also increases your team's objective control and makes things like Baron a less risky affair. I'm not saying it'll be the go to for everyone, just like how TP/Smite isn't the go to for every top laner.
I could also see the benefit of stalkers, less so, but still, I know it'd be handy to be able to chase better on a Diana to get in range for ults. Can you imagine how impossible it'd be to get away from Fizz with stalkers? I think it's not too far fetched to believe that it'd be a useful alternative with a mana regen component. Frankly I can't tell you how many times I've had our team lose objectives because of poor smiting from the jungler. Just think if you had Nunu, Cho'gath, and say Shyvana. You essentially have 5 smites on your team, the counter jungling and objective control would be absolutely brutal. Even just Nunu with two additional smiting team members. The enemy jungler might as well quit because he'll never get a buff.