In the one I suggested a while ago, the changes would usually affect the maximum tech levels for things, and broad laws of physics.
So if a wave of "low tech" sweeps through, then shields will stop working and any weapon above some arbitrary level will fizzle out.
If it gets really bad, then warring ships may be reduced to ramming each other for a year
The occasional wave of QNP/normal/inverted QNP would be interesting too
Even one where speed is independent of engines!
"Um, sir? Our scientists report that the latest quantum storm has resulted in larger ships having less momentum! Our escorts are dead in the water!"
The ability modifications should be fairly general changes, such as "all beam weapons do 2x damage", "All supply usage is squared", "All missiles have infinite range" and so on.
This sort of game would still work well if hosted by PBW, just with the game master processing turns manually.
[ May 11, 2003, 16:16: Message edited by: Suicide Junkie ]