*Membership spots not really limited!
Ord might be tied up with the X-Men stuff, I don't know. And if not, it wouldn't be a horrible choice because it's the first alien race in a movie (so they don't feel like ripoffs), they won't be replaying the Shi'ar stuff (since it's never been done, and there's no X-Men), and they'd just kind of take the place of the Shi'ar as one of the many random alien races out there (since the Shi'ar are almost certainly tied in with the X-Men). So this gets the cosmic ball rolling, then you can use the next set of movies to bring in Skrulls or set the stage for a Kree/Skrull war or Ultron or whatever, and these guys can be fully defeated.
That said, it would be a disappointment to see them instead of someone actually cool.
I think the idea that's a giant dragon (Fanfir or the Serpent or just a random unnamed dragon) from Asgard and his army is Dark Elves or something, makes a lot of sense.
I think the idea of him recruiting aliens also works, but would require a little more explanation.
I think if it ends up being Atlantis, I will not be able to deal with it. Especially if Namor shows up to save the fucking day. That would melt my fucking mind.
Well gotta remember the map in Iron Man 2, with the dot in the middle of the ocean, one of the dots was thor's hammer..