I'll be a naysayer here and argue rather that a large expansion of possible NPCs rather than a raise in party number would be far more preferable, particularly with interactions between NPCS (Like Shadowheart and Lae'el and how Shadowheart leaves if Lae'zel joins) would be highly preferable to me.
I do like when party members get mad at each other and leave, but there are far fewer companions this time around so losing one is a much bigger blow. Also, with a 4 member limit, you drop 1/4 of your party when someone bails until you go back to camp. That's a crippling blow.
6 party members actually supports characters leaving better. Both because you have a larger team that can take the hit, but also because you are more likely to have NPCs at the same time who conflict with one another. Drama!