I can't see Eminem doing Coachella...but then again I never thought Dr. Dre would either. Something about Jay-Z & Kanye felt alright - I guess they both have more connections to other Coachella artists/music styles, or their style of hip hop is more laid back. Eminem is so angry and violent though, it doesn't fit the paradigm to me. I felt the same about Dr. Dre though he's also way more legendary than Eminem (in my eyes). Whatever, anything's possible I guess.
Edit: I just saw a Green Day blurb and this whole 3-album thing...it's almost like setting them up to headline. I don't really pop-punk (headlining!) at Coachella but whatever.