With the news of Nexus Blitz no longer being a permanent game mode I feel like Twisted Treeline could be an amazing replacement if done right. Twisted is already a permanent game mode but it's unbalanced and dead. It's a fun game made to play a quick game with a few friends if only you didn't see the same couple broken champions *every game*. Funneling is still a problem, not to mention indirect nerfs/buffs that happen like ghost poro (which was meta defining in 3v3), and Vilemaw is a joke of an objective that feels *bad* to use because it messes up waveclear by fearing minions out of waveclear spells for mages.
If Riot wants a quick more laid back gamemode (like blitz) then Twisted Treeline is the way to go. It even has a rank system for those who *WANT* to get competitive about it. If they just put some resources into it, it could be a really nice game mode.