While the letter of VATSIMs rule is fine, in my experience as an ATC on VATSIM, the sentiment passed on was to only handle emergencies so as long as it didn't affect other pilots enjoyment. This is where we may have diverging views and need discussion and clarification. Say I was on TRACON and a departure had engine failure on takeoff, requiring vectors to join the approach sequence. Fine. Do I force aircraft already sequenced into a holding pattern for a few minutes to accommodate the emergency? Would it affect other's enjoyment? Some would love the unpredictability and having an experience they don't normally do (being taken off an approach and put in a hold), others would be frustrated, just wanting to finish their flight without interruption.
I think that emergencies can bring a greater sense of realism and enjoyment for everyone. It's part of the deal that when you log into an online environment, things aren't in your control and you have to be flexible. So I think ATC should provide priority to emergency aircraft, even if it adversely effects other planes. I do not think we can extend this line of reasoning to shutting down a runway for more than a few minutes because an airplanes is unable to taxi. At that point everything is grinding to a halt and we would need to some way to deal with that.
ATC having right of refusal solves a lot of the potential problems, but I think we should make sure that we specify that if ATC is letting the emergency happen, which they should if the pilot is a non troll, that the plane be given priority even if it causes other pilots delay and inconvenience.