Wasn't HDMI 1.4 meant to do this on a single cable?
http://en.wikipedia.org/wiki/HDMI#Version_comparison
I guess the limitation is 24p for HDMI 1.4, so if you want to use it for anything than 24p movies, then I guess I've answered my own question
Apparently DisplayPort tops out at 3840 × 2160... so much for future proofing...