But that problem might be acceptable if it's an option you take at your own risk. I'm not a fan of the bigger party because a) in my opinion a professional approach needed a lot of balancing and additional design of the fights (aka Larian's time) and b) I'm lazy and normally don't want to play even more classes. B) is personal bias and of no interest if it's an option between 4 and 6, A) wouldn't be a concern if it would be a very easy change for Larian. If it's not entirely balanced, ok. I also have to admit that lately sometimes I wouldn't mind to have 5 in the party, to have room for Lae'zel (or a Fighter mercenary) in addition to my boring normal team.
Perhaps however my thought that players would accept a not perfectly balanced gameplay without flooding the forums with complaints about the life destroying effects of such an approach might be rather naive.