Personally, I'm less concerned about spell levels and mechanics than having a story that justifies higher levels. I think of someone reaching level 20 as being the culmination of a career, after years of different adventures, so going from level 1 to 20 in one game isn't really something I want unless it is ridiculously huge and spans many years. And in gameplay terms, I don't like levelling too quickly and prefer to get the opportunity to experiment and use the abilities I get at different levels.
I'd be all for an expansion or DLC, or BG4, that could take us to higher levels, but I am very glad Larian didn't try to cram more levels into BG3. And even if we don't get those expansions, then I wouldn't want the pacing of increasing levels in BG3 to be any higher than it is now, though admittedly I'm still only at level 8 at the moment.
