Uh to the main topic, even though they didn't envision BG3 as this, I would like to see it be a 1-20 Adventure, or ending somewhere around 1-14 or 1-17. This would allow full character progressions and allow for over the top or big combats near the end. It would also enable a large variety of magic items that can be powerful, and multiclassing would feel somewhat rewarding if you choose to do it as you have levels to work with your concept.
That's fine to want; who doesn't want to take an RPG to its highest levels? The question is would you rather have a game in 18 months and an expansion a year or 2 later, or just wait another 3-4 years whilst they develop tools for and balance dozens of new feats, new spells, weapons, armour, and then iron out the hundreds of bugs and unintended interactions that all brings?
Not to mention the fact that higher level spells are generally several orders of magnitude more intricate in how they affect the game environment than, say, Firebolt. And we will want new snd intetesting maps and locations to gain those levels in. And an expanded story arc. We need to have realistic expectations of what is possible.
Failure to do so tends to go one of two ways; either a game is rushed to launch and experiences the kind of car crash garbage fire launch Cyberpunk did; or it spends forever in development, gets labelled as vapourware and anyone who preordered or bought early access starts thinking about refunds, like Star Citizen.