Apparently I've seen this type of stuff before, I just didn't remember or missed it.
The Gorillaz did some hologram performances of Feel Good Inc., and at some point a hologram of Elvis preformed an "If I Can Dream" duet with Celine Dion on American Idol.
The Gorillaz performances could be 2D projected onto a flat area for all I know, but I think they are in fact holograms. The Elvis thing is weird, it looks like a real guy, but the face looks like it has that low quality of coming from an old video, making it almost look like Elvis's face on someone else's body. Maybe they combined a recording of an actor and Evlis's head to create the entire hologram.
I want a hologram now. I'm not sure what of and what for, but I want one lol.