I very much hope the party size increase mod gets updated and remains available (and is brought to Steam Workshop). My already-very low interest in playing the game will drop all the way down to zero if I cannot play with a party of six.
Pretty much this.
Later on I'll want the ability to mod Withers to allow for fully customizable characters (assuming hirelings can't be entirely redone), but that can wait for a second playthrough. Meanwhile, without the way to play with a party of 6 then entirely a non-starter for me. I'll just wait to buy the game until the mod is updated for full release.
