Not more team slots, but more distinct ‘memory’ of the team slots for different aspects of the game.
Currently the game remembers your last team slot used for raids, titans, current tournament, and it even remembers the previous challenge event and trial teams. Everything else is lumped into the last slot. I would like to see quests and S1/S2/S3 each have their own team memory slot. It saves time and the annoyance of making minor team changes or scrolling back and forth. S1 farming obviously needs no 5* healer that S3 hard modes use.