We had ARAM, we had URF, the closest we've got is ascension...

So can we please get a game mode which is just a 1 life 3v3?

Similar to the Battlerite theme. Just set levels to 18, max all skills automatically, and if some champions feel too useless for one reason or another you can add a few items automatically to help balance things out a little.

Put it on the ascension map, and just auto TP players into the middle after a 30 sec buffer or so.