So far Larian has been implementing extra attack as extra full action - that’s what I worry they will do for full release and that would disasterous for casters. I doubt they will implement multi action as in written rules - the game just doesn’t seem set up for that. A simpler solution would be to add “1 spell per turn” rule to limit fireball spam.
Yeah, honestly the "only 1 leveled spell per turn" from 5e would fix most things.
You do need to be careful about the interaction with quicked spell (which btw has to have its cost reduced to 2 SP again) and also still about valor bards, although honestly their cantrips are so bad it probably does not really matter...
