I think that party of 5 is the most balanced variant - it can allow to cover party basic roles (arcane caster aka CC / AoE damage, divine caster aka healing / support, tank, single-target DPS) and allow main PC to play any class they want to complement it. As far as I know, there are also 8 planned companions, so 4 companion slots make perfect sense - game can still be replayed with totally different set of companions. It is also not a very big increase to player party power (around 25%), so maybe Larian would not even need to rebalance encounters much to adjust. Something like: Current game design for 4 party -> Easy difficulty for 5 party (so they do not even need to scrap it) Their planned hard difficulty for 4 party -> Medium difficulty for 5 party (so they do not need to scrap it as well) More enemies / harder stats / additional abilities for them -> Hard difficulty for 5 party
So, the only additional work Larian would need to do in addition to already planned is change party number to 5 and implement "hard" difficulty for 5 party.
Though, many of these points could be applied to party of 6 as well, but it would require more work to balance the game for that.
