Well that is a complicated question. But to start with, 99% availability of the servers (or whatever the industry norm is for MMOs), no desync issues and having the ability to set the client to full screen without having to manually edit the ini would be a start. Hard to say more before I tried the game :)
But I assume that by the time you release it on Steam it would be somewhat ready?
And kudos for not going 3D combat. That is just confusing and makes combat more like a chore than what is should be, which is a space opera :). I loved Sins of Solar Empire and this game definitely have the same vibes to it but with added persistence. Awesome!