Returning Baddie for 50th Anniversary

According to one reliable source, Omega is returning for the 50th Anniversary. No actor has been confirmed to play the role of him yet. They could just be keeping it a secret (they managed to keep Jenna-Louise Coleman's appearance in Asylum secret) or it could be someone we already know about.

The classic series actors have all denied involvement in the 50th anniversary. I frankly think Moffat isn't stupid enough to not include them in the episode. I think either Davison, Baker, McCoy, or McGann (or some combination thereof) is going to play him. How? In the 1983 episode The Arc of Infinity, Omega stole the Doctor's biodata and duplicated him in order to create himself a body. He may still have that biodata and may be using it for another body (his original one was destroyed in The Three Doctors).

If it is a new actor, it's not going to be anyone we saw in location shooting. The BBC is going to want to keep it a secret, so all of his (or her) scenes would be filmed in Roath Lock studios. They're keeping everything very hush-hush, so we'll likely not get any new casting details for months. The only cast the BBC's announced has been those who were location shooting, and only then right before the actual filming. They're revealing as little as possible, but keeping all the glory of the announcements to themselves.