Hey Riot, now that you let ADCs go in other lanes

Not gonna happen. At least not without MAJOR systemic changes to the way League works.

Ranged, auto-attack based champions are the prefered kind of champion in an XP-sharing lane, for the simple reason that these champions are the least negatively affected by sharing experience. Ability-focused champions need XP for the base damage increases and benefits from ranking up their abilities, whereas melees need the base stats from additional levels.

I feel like they've tried this once, with some worrying results..

Making this work would require massive systemic changes to both how objectives are taken and how XP is handed out on Rift.