I would then suggest making a Party of six for/as an EXTRA Mode called f.e. like LEGACY or similar and reduce the Character interactions to allmost ZERO.
No more Story Content for the 6 Mainchars. Treat them like you would have 6 Custom Characters. But then theres the Problem about Character Storys like with Shadowhearts Artefact etc. Those must be rewritten that those items or Storys are somehow connected to our adventure but found or introduced by another way in this LEGACY mode.
All Ideas which can bring this Gamemode on the run, make it work, can be either made by modders or Larian himself. But i strongly think it would bring the classic RPG feeling back for many people even myself (also played Curse of the Azure Bonds in the 80ies last Century on C64). But dont make it have autobattles which take more then an hour