writes:

Maybe you can get VATSIM to require a diversion to some other
unexpected airport at some random time during cruise, to spice it up.

That is determined mostly by the weather, not VATSIM.

Or, how about simulating an instrument failure, or loss of
communications.

Occasionally people simulate emergencies on the network; in fact, they have a
lot more simulated emergencies on the network than you would expect in real
life, especially improbable things like multiple jet engine failures.
However, these are often the kiddies on the network who have the wildly
improbable emergencies. I simulate emergencies about as often as they occur
in real life, and so I have yet to simulate an emergency thus far.