The main issue I see with increasing party to 4+ is that the game is not being built around it.
Please define for me "not being build around it". O_o
Are you adressing problems with combat dificiulty? > Allready talked about, as long as party of 6 is OPTIONAL (wich is what most people want here) its not a problem, bcs people who will want it will be notified that difficiulty of game will be affected ... and people who dont mind will not activate it ... sure there will be people who will activate it anyway and then complain that game seems too easy, but you cant save everyone, especialy not those who are swimming in acid and cry "it burns".
Are you adressing UI issues? > Larian actualy (paraphrasing Swen himself) "count with the fact that 6member party mod WILL be present for many players and preparing all UI to be as possible to adjust to it as it can"
Are you adressing problems for some players to operate with more characters? (I honeslty never understand this argument, its turn based, you allways use only 1 character at the time) > Again not a problem ... if rule (as we ask) will be optional ... is party of 6 too much for you? Set party of 5.
Are you adressing anything else? > Please tell me, those were meerely FRC ... frequently repeated complains
If my comments bother you, there is nothing easier than telling me to stop. I mean ... I won't ... but it's easy to say.