I think there were issues with mixing the different UIs in certain circumstances, which would have taken too long to try to fix.
You can run two copies of the game (or can with D:OS, anyway), but I don't know if they would support LAN co-op that way.
Thanks for your fast response! I also lurked here somewhat and am amazed to see how patient and responsive you are, I have yet to see any other "community managers" like that anywhere else, although granted, I've only been to around 20 or so places.
Btw, I cannot find the PC EE available anywhere to buy, so I assume if we buy the original before the 27th (even if on the 26th), it automatically gives you the EE?
I hope you guys manage to fix the UI clash soon after release! I'll try test the double process workaround when the game is released, since it isn't possible to test with the base version without controller support.