There’s an article in Entertainment Weekly about Adewale Akinnuoye-Agbaje (Mr. Eko) being interesting in making a return appearance in LOST.
I seriously doubt this is going to happen, not only because of the way he left the show and because of the friction between the stars of the show, but mainly because I don’t think it will fit in with the story from here on out. I think there’s as much of a chance of him returning as seeing Nikki and Paulo coming back.