That's a bad poll, because it puts the question in a very unclear and questionable form. We don't want "the option" to add two party members as some sort of fancy extra. We want the game to support a party of six as a default interface and then let people who are happy with less party members do as they will.
Precisely this. Your options should simply have been something along the lines of:
6 - As standard (but players can choose to play with fewer) 5 - Cap it here, its a fair compromise 4 - It's fine as is and Modding can do the rest