I would question the need for a giant hotbar in BG3 to begin with. BG3 is not a real time game where you need to be able to do everything with one click. It's much more important things are in a logical place.
Solasta has no hotbar at all, and it works wonderfully. It's clean and intuitive. BG, Pillars of Eternity, Pathfinder.. none of these games rely on huge hotbars. NWN has a 3x12 slot hotbar and it's good there because it's real time without pause in multiplayer. I like the quick accessibility of more hotbar pages with CTRL and SHIFT which means you don't need a million tiny quickslots on the screen simultaneously to save space.
Spells especially need their own UI interface that sorts them by level, upcasting and metamagic. I assume Larian simply has to create a functional spellcasting interface by the time Sorcerer comes along with both metamagic and upcasting versions of every single spell.
