My solution to fixing the jungle forever, while allowing nearly every champion to jungle: Instinct

Instinct is a special stat or buff that your champion gets when they enter the game with Smite. Tooltips would have a greyed out extra portion that would highlight and be readable when Smite is selected.

Primarily, Instinct will increase the damage various spells will do to jungle creeps, although it might also affect auto attack damage. For example, let's say we want to make Annie a viable jungler. Well we edit her abilities with Instinct, to make them gain +x% dmg vs neutral monsters when Annie takes Smite. You can even custom-tailor it to specific abilities, so that, say, it's Molten Shield that gets the damage increase, so that Jungle Annie has to invest in Molten Shield so that her ganks are a little less damaging, or so she needs Molten Shield available to really take on a camp (like Sejuani needs W up to take on a camp).

We've made Annie able to clear the jungle and put her into this new role. But maybe a point and click stun on a gank and all that damage is just too good with how safe her clear is. Well, since we have this nice new Instinct lever we can adjust, we can dial back her jungle power without affecting lane Annie at all. We can make her clear faster, slower, safer, more dangerous. Let's say it's Poppy we want to make into our next viable jungler. Well, if we increase the damage her Q deals to creeps, we'd have to make it so huge that she'd probably be one shotting them. So...maybe make it so that W blocks extra damage from jungle mobs, and makes her do more auto attack damage to them, too. Voila.

Each champion has some way they can be adjusted in order to custom fit them to the jungle.

Jungle Morde: Creeping Death deals increased damage to jungle mobs, and Morde's passive has a better conversion rate vs jungle mobs (he gets more shield from jungle mobs than he would vs players/creeps). Boom, Morde can now Jungle.

Braum's Instinct can grant his passive no cooldown versus jungle creeps, and increased damage if he needs it. If he's still unhealthy, it can restore some HP to him when he procs it vs jungle mobs. Boom, jungle Braum.

Irelia: Hiten Style is changed as needed versus jungle mobs--half damage even when it's off cooldown, maybe. Killing a mob with Bladesurge grants a bit of health back, too. Whatever.

Zilean: Jungle mobs hit with Time Bombs have their attack speed slowed for 5 seconds, and Zilean's attack speed increases for 5 seconds. Zilean does x% of his AP as bonus damage to Jungle mobs (this one would probably be a popular Instinct for AP champs with long CD abilities.)

Pro:

• Anyone can jungle. You can basically sit around and come up with a way to tweak any champion versus jungle mobs and have them come out as a viable jungler.

• This can be a tool to regulate actually good junglers, too. Warwick's sustain can be easily tweaked versus the jungle. Jarvan's clear time can be acutely selected.

• Changes to Instinct will not affect that champion's laning game. You can nerf Jarvan's jungle without buffing him in lane. You can buff Riven or Irelia's jungle without allowing them to run roughshod over top lane.

• You can do away with jungle specific items entirely, if you want. Or, you can just make another stat on items that is only visible to people with Smite, which enhances their Instinct bonuses. Whatever.

Con:

• Anyone can jungle. Some champs are literally designed around their position in the jungle, and this takes that away from them. Also, some champions should just probably not jungle. Like Alistar.

• It feels weird for "instinct" to make people better at the jungle, when champs you would expect to be awesome at fighting the jungle, actually have very little actually changed (since they're already good at it).

• It's usually a bad idea to have a bunch of "shadow stats" that only come into play under certain circumstances. It's hard to understand for newbies and power levels will feel "off" between fighting mobs and fighting champions.