Well, as for Larian's next title, I suppose the one thing they shouldn't do is Early Access. Like, at all.
Their development has always been tumultuous and messy as-is (what with constant rewrites and redesigns very late into the cycle causing everything to come apart at the seams, BG3's just the most obvious example because of how oversaturated it is), and if BG3's EA has shown anything, it's that they can barely maintain a stable vision of what they are trying to cobble together, and you add the player feedback on top of that which they stopped giving a crap about around a year before release, switching to appeasing the "slobbering over a somewhat poorly written globule of pixels" crowd instead...
...Oh, right. Remove romance entirely, please. Altogether. Either make a full-on Subverse-like if you're so commited to slapping sex on everything and everyone, or ignore the subject altogether, because BG3 certainly was anything but a smooth mixture of tones.
And maybe focus on the PC playerbase first and foremost this time around, the, well, overwhelming percentage of whoever even plays CRPGs? Proper mod support on release and not spreading resources to try and squeeze the game onto a brick until a year or so after it comes out worked just fine for D:OS2.
And no need to rent castles anymore, perhaps. That budget could have gone into much, much more pressing matters. Like character customization that isn't embarrasingly simple for a cinematic CRPG. Or not having your AA settings reset every time you launch the game if you're using FSR. Or slings. Or belts. Or proper reactivity....