multiplayer isnt possible on the itch version as the multiplayer will be running on steams api. giving out keys to anyone that bought the game on a different service would be against steams tos as he would be avoiding the 30% cut.
Against tos? Where you got that from? If that was the case so many other devs who have given away keys to itch.io supporters, resell them via humblebundle, inc triple A studios, would be in breach of this “tos”.