Downvote me if you want but Im going to say it:
Twitch is only stronger because of the current Masteries and Ardent Censor.
Why Ardent Censor? Because when Twitch ults, every target hit has Ardent Censor's passive applied to it, meaning Twitch abuses the item the most out of every ADC. With it being the FotM right now, this just makes Twitch all the stronger. In addition, the current Masteries present, namely Warlord's Bloodlust and Fervor of Battle, help Twitch a ton and also synergize with his ultimate. Basically, Twitch just abuses everything that is currently meta. When preseason hits, unless they add back in a Warlord's Bloodlust or Fervor of Battle keystone rune, Twitch is going to most likely be nerfed due to this loss of synergy and, if Riot nerfs Ardent Censor (hopefully they will), Twitch will be hit the hardest due to his synergy with it.
Basically, Twitch needs to only be hit by small nerfs if any if he is to be changed right now. If Riot nerfs Ardent Censor and doesn't re-add Fervor or Warlord's in Runes Reforged, then Twitch WILL BE INDIRECTLY NERFED ANYWAYS. I think it would be better to slightly nerf Twitch in the mean time, and hold out on significant changes until we get to see how Riot deals with Ardent Censor and how the preseason plays out.
Nerfing his base stats, like base AD, armor, and health, would be a nice little change to keep him in check, but not obliterate him due to him simply synergizing well with the current tools available that will most likely be changed or removed in the relatively near future.
Something like...
Base Health: 525 -> 500
Base Health per Level: 81 -> 78
Base Armor: 23 -> 21
Base Attack Damage: 55 -> 52
...would be nice and suitable for now until we discover if he is still a threat after the predictable Ardent Censor nerf (or even rework) and changes to Runes and Masteries.