I don't think netplay would be that hard to do. Not when you compare it to making the actual emulator that is. Remember the xbox already nativly supports system link, which simply connects to an IP on a local network. So all the emulator would have to do, it redirect that to a specified internet IP. Compaired to ther other work on the emulator it's quite likely one of the easier things to get done.
Of course things like internet smash bros would be way harder since that game doesn't support system link, and you'd actually have to do something pretty complex to allow player 2 to be remotely connected. I don't really expect to ever see that.