Swen mentioned Multiplayer and the reasoning for 4 man party in the Dropped frames interview, if you are curious.
In short, it's for stability and balancing purposes. If you want more party members, you will have mods.
I hate large battles at the moment, I can't even imagine I'd be running around with a party of 6 right now.
The only thing I would hate about having a six men party right now is that party controls are utterly atrocious and need to be fixed.
But that's true even for a four-men party, so let's fix those.
Anyway, this is all stuff we already discussed more than once and the thread about this specific topic is quite literally the biggest one in this sub-forum (at least until the trollish one about skimpy outfits will surpass it too).
Contributing to existing threads instead of starting new ones on the same arguments would help make the feedback a bit more focused... For how little it may actually matter.
Large battles are far more fun with more companions
Easier maybe, the AI is all over the place with larger battles, that's why I hate them.
Which is a separata argument, more akin to a technical issue than a design flaw AND something that wouldn't get worse with a six-men party (in fact, probably the opposite: the player would have more chances to inject his actions in the middle of long queues of NPCs thinking their moves).
