During the first weekend of the co-op me and my friend encountered some server issues. One of us had kept losing control of their character when the server lagged and the other kept getting kicked back into main menu. Having no control over it didn’t feel too good especially since our free playtime during the weekend overlapped with the issues encountered. Thankfully the co-op test got extended 
I’m aware this is the first open test to this scale and issues are expected.
We still would like to suggest making the option of self-hosting realms be made available to players that care for it. We would feel more comfortable hosting our own server and having full control of it than being completely helpless if anything happens to it.