How to go about it? No idea, really - but as a player who found S5 to be the most enjoyable season by far, I'm gonna give it a go anyways!
1. Remove all the keystones - balance around champions instead. Let us choose a 3/2/1 setup from minor runes from different rune paths. This should alleviate a good bit of the burst and cancerous playstyles - also make Zed actually have to land his abilities! :P And as a bonus, should make the game far easier to balance in the long run.
2. Remove Duskblade dmg addition, maybe replace it with something "visiony", due to later mentioned vision ward changes. Remove Stormrazor completely. Revert Essence Reaver changes. Balance accordingly.
3. Nerf pure tanks damage, but increase their survivability. Plenty of ways to do this healthily.
4. Lower plating gold some, and keep them the whole game. Possibly have plating on inhibitor and nexus turrets also. Should make the game longer, and have IE/ER + Zeal item upgrade be doable again on "standard" ADCs. Maybe radically buff nexus turret dmg.
5. "Un-buff" ignite.
6. Reinstate season 5 vision trinket upgrades and possibly boot enchants.
7. Slow down on the minions winning games please.
1. Shutdown gold - I had a game where we were at a 4k gold disadvantage, but then we got some lucky shutdowns and objectives, and we suddenly had a 3,2k goldlead within 5 minutes. Don't know if that's all that healthy tbh - but maybe spread the shut down out over "multiple" kills could help that.
And a few pet peeves of mine I'd like see changed, but are not to be taken too seriously:
1. Nerf high mobility users some, please - high mobility while sacrificing nothing, damage/survivability wise is just stupid.
2. Nerf Akali's new shroud to regular stealth. Then balance around that - we dont need more frustration in this game.
3. Revert Malzahar completely and THEN "Annie" him instead.
4. Griveous wounds - can we just remove this crap, and rebalance problematic champions around that instead, as GW is the difference of those champions being OP or UP in the same game - why not the golden middle road?