Just throwing this out here as it's my first post and I need to get my post count up before my official suggestion post.
No official name yet, but is there any interest in an OM where the only pokemon allowed are OU pokemon (The pokemon in OU in that generation are essentially a time capsule and the pokemon included are ones before any major Tier shift at the start of a generation's meta [Think Dracovish and Mega evolutions in Sw/Sh, Celebi in gen 2, etc.) The OM is subject to shifting to a different point in any given generations meta, subject to user voting.
I think this metagame would be perfect Generation 6, where it seemed like Mega Pokemon were getting constantly banned over time. Every time a Mega was banned, a weaker one would become prevalent and usually get banned. Mega Kang, Lucario, Mawile, etc.