If everything I'm reading is true, here's a summary of why jungling is going to suck in season 5:
Buffs spawn later, so you either won't get a leash or your allies will be much later to Lane or go to Lane and come back to give you a leash.
Buff alone isn't enough for level 2, meaning the jungler has to clear an extra camp at level 1, many junglers need 2 skills to clear camps effectively solo (why the leash is so popular).
Combination of these 2: junglers won't get the instant level 2 head start and first to level 3 advantage any more, even though solo laners already reach 6 before them. Junglers will now be either similar level to or possibly lower than the duo Lane throughout laning phase.
Result of this: with smaller gold income and a level disadvantage, junglers will only be successful when ganking a really out of position laner. Against any experienced player, ganks should be unviable - meaning junglers can't get kill/assist gold/xp, putting them even farther behind.
Camps are being made stronger, are spawning less frequently, and give more gold (but recall above buffs give less xp, not sure of other camps). Stronger camps combined with the level disadvantage might prevent early game jungling all together, requiring leaching from lanes (which your laners won't like) before being able to clear the jungle. Those few junglers with enough sustain and damage to actually still manage jungle clears despite fewer health pots won't be able to just farm the jungle as they'll need to wait for camps to spawn.
It appears that the conservation stacks are being removed, resulting in even less gold income.
The new vision objective will give junglers something to do when camps are down, but will again take away from time that could be used to earn gold.
Benefits:
The new jungle items, with the improved smites and enchantments, sound much more useful.
All junglers will suck equally (at least until someone finds out the 2 or 3 that can Excel in such a poor and rough environment) so it won't always be Lee sin vs kha'zix (even though honestly I see other junglers just as frequently).
I'm just really hoping it's either not as bad as it sounds or riot fixes the issues here. I'd much rather go against a lee sin in a jungle I can actually compete against the laners with than be a jungler where neither team's jungler can do anything at any stage of the game...