I don't see one good reason for limiting companions to one,
You don't think play balance is a good reason?
Or do you feel that, in addition to a multi-companion system, they should also make the level scaling system capable of going "Ok, it's a party of X people, multiply monster spawn difficulty by Y"? (which, of course, would actually be much more of a complex issue than that simplistic example).....
(And I'm sure this will aggravate some people, especially the ones who take the "do what you want" thing a bit too literally, but.... if you want to play a "direct an adventuring party" game, why not play a game actually designed for that? There are plenty of RPGs out there that are built around having a party of 3/4/5/whatever. The Beth games I've played so far have always seemed like they were better suited to "lone wolf" style play - the companions have always seemed to not work well in the framework of the game. But, hey - maybe that's just me. :shrug:)
Bethesda shouldn't really bother with companions anyways, Obsidian did such an amazing job with them in NV, making them actually useful and with a good backstory
Like I said earlier - I really disliked the companion system in New Vegas. Specifically
because they were "deeper" and more developed - they had so much game content tied to them that I felt forced to drag the stupid things around with me, even though I really didn't want them underfoot. At least Fallout 3's companions were much easier to ignore.