It would essentially be like side-by-side PIP, displaying two inputs simultaneously. The hardware might not have the capability of being able to accept two simultaneous streams simultaneously.
If that doesn't work, there's a Plan B. This is a perfect hacking opportunity: I bet someone can do it with $300 of add-on chips (Xilinix FPGA's, microcontrollers, HDMI 1.4 receiver chips) -- this is a perfect market for an add-on mod. Mark it up by $400 and sell the board for $700, then you've got 3840x2160 at 60Hz for $2000 total. Still a steal compared to other competition costing $5000. (Scribby? Hypermatrix?) Clearly, the panel is capable of being refreshed 120 times a second, so there's already enough panel bandwidth and the board/HDMI is simply the limiting factor.
That means, theoretically, the panel could do 3840x2160 at 120Hz using quadruple inputs, given the right custom motherboard (probably still costs under $1000)!
As we can see, the thread was hijacked on page 1 some 3 years+8 months ago Cirthix is definitively posting on the relevant thread [H]ere.