You acknowledge fact, that it was mentioned times before, but you still write about it? I see no sense in that.
But anyway, I'm more than sure, that devs perfectly know, that co-op could be good for game, but I'm also sure, that it's too big thing for them to make. Honestly, I don't really have faith in devs, they a little disappointed me with Warband (when compared to old M&B) and with WFaS(crap-game, which they just touched, instead of totally remaking, what should have been done...).
So I don't think, that they would be able to make co-op right.