Yes, it was possible to play the main campaing of NWN with a friend or 6 friends (max 16).
I do not share your opinion. The main mechanics would not be affected in any way! That's why I suggested a "host-forced" progression of the quest book - which is already the way the game works.
As an electrical engineer I am capable of coding and I know its not that hard to implement. But of course it does take time and therefore costs money. However I am not sure if the engine can handle it, but I would be very surprised if stats and equipment (basic values) could not be overwritten when joining. If it is anything like NWN the stat-values will be compared when you hit a trigger-point. I do not see any problem with overwriting those values. Remember, story progression is still forced by host (no changing values), as it is already and any situation arising should compare values at that trigger-0point. So you would not break any game mechanics!
