I would like sub class + school specialist too.
You take blade singer you get blade song, 2 attacks +cantrip and song of victory in it's appropriate levels. Get evoker and get sculpt spells +int to damage and overchanel. It would spicy things way up, give a ton of combinations, open themes for sub classes and make other classes get something cooler from what they a getting to balance everything.
I do think subclasses+ specialisation should be the way forward for everybody.
Warlock already does that with blade chain and tome. New cleric does that (badly). It would enrich and give something to look for every other level.