Hatsune Miku is also a projection, not a hologram. But I think it's "further" than you think, because every single song at the concert is created by a musician or team that releases the song online for free. The extremely popular ones are put into the concert, as a way of saying thanks by the company who makes the voice synthesizing software to the fans.
In Japan, this has been taken further. No live performers at all. Here's a Vocaloid concert:
http://www.youtube.com/watch?v=dhYaX01NOfA
Both the image and singing in that video are entirely synthesized. Rock stars are headed for the unemployment office.