
The hack of coming up with splitscreen outside the game would be to start multiple RWRs, make one a server and join the others in the first. It is possible up to this point easily, had to add 1 line to make the windows keep updating rendering when out of focus.
Input handling is a problem though as only the focused window gets to handle the input. It might be possible to make OIS behave so that it captures the input regardless of the window being in focus or not, frankly I have no clue at this point. Having two mice could be a bigger issue though as there are some rumors DirectInput doesn't support multiple mice, but then again, the stuff I happened to read was from 2008.
Anyway, in-game splitscreen support will most definitely not happen, the amount of work compared to the demand for it wouldn't make any sense. I'll do the things I can to make it possible with multiple windows, but even then it's very low priority, and might not be possible at all if the mouse restriction is correct.