And now I have to ask, "Would it really make combat so much slower to add 2 more party members?
The way they muddle up things, yes it will. They will probably end up adding more health to enemies or adding more of them to each encounter if they change everything for 6 party members because they feel it is balanced for 4 currently and 6 would make it too easy. Adding enemies especially will make combat even worse than it already is for those of us who like stealth gameplay (or what passes for it here.) I have actually found solo play to feel "faster" in the goblin camp simply because I can go and do other things while the enemies take all day to do nothing on their turns. Having to sit and stare at the screen because my party has to take their turns already makes it tedious enough with 4.
If they were to keep things as they currently are and add an option for 6 party members then I don't care.