One of the reason why seamless coop is so good is you can play with mods without having to go offline and disable anti-cheat. I fully expect their implementation of this won't allow for that.
The fact that I can't do something as simple as turning off that god-awful chromatic aberration without anti-cheat banning me for cheating is so ridiculous. It's so bad that I only play offline and at the moment, Seamless Coop is the only way I can play multiplayer.