it could be interesting if it was possible, it could be like playing command and conquer coperative.
the file should be handled and saved by the session creator in order to prevent stealing like any cooperative game onlyne. also I think the crator of the stage should define areas where any of the players work, so the other players could not mess with what you have already done, also the arquitect would have right to undone or erase what other players do, I think also, that the maps should be able to be done logged in only, so the name of the creator would be displayed on a preseted 3d bildboard in game with all the supporters.
it could be most possible to be realised if using only models or items available in the defauld tool, if so,
when the file is saved etc ot would not affect what the other does, the file update would be just a matter of reading few data and loading from the file of the main participant.
custom models would be complicated to load, because it would need to transmit the data to all the rest of the participans and would be likely to crash or desync anytime one has loaded a custom model and the other player needed to update the file etc, it would not be imposible, but a bit complycated to prevent glitches.
