Well, not a game centered on them or anything. Just maybe a quest or two in the next installment is all I'm saying. I think Zeta is focusing more on combat with them and not storyline of the aliens.
See, I'd just as soon they don't supply any story to the aliens. Honestly, what I would most like from the Mothership Zeta DLC is a sort of "Fire in the Sky" thing. ie, you get abducted by aliens for mysterious purposes you see some creepy things (that still give me shivers to this day,) and then you escape.
I'm of the opinion that the more mystery the better. And as far as quests in Fallout 4 - well, with MZ they'll have already played the "abduction" card. If they were going to keep it mysterious and ambiguous; then I don't really see what else they could do with it. (Brahmin mutiliations, maybe...)
Hey, that's just me. My opinion is that the trouble with good mysteries is that the truth is almost always an anti-climix. (For example - that's why in a good horror movie you don't see the monster until towards the end. Because you can only play that card one time. Once you've got a look at him, he won't be scary the second time around.)