I personally wouldn't need it (like I didn't need Turn Based mode for Deadfire) but if it's possible I would totally vote for it. I mean why not? Doesn't hurt to have more options and the more players the better. No idea if it's doable with the very specific game engine Larian uses - but maybe this could come as a patch or DLC? Or would that be off-putting?
It won't salvage anything.
Fanboys will be fanboys.
If Larian changes the battle system, the toxic fanbase will cry about the UI.
If Larian fixes the UI, they will whine about the music.
If Larian changes the music, they will whine about the assets.
If Larian changes the assets, they will whine about the game's tone.
If I was Larian I wouldn't change a single one of those things. It would simply be a waste of time and resources. For changes, I would focus my energy on the gamers who talked about what works and what doesn't in the actual gameplay mechanics used NOW (i.e. shove being overpowered, percentages being misleading, etc.)