Here's my most recent idea on the subject of running multiple servers on one machine.
Extending this functionality without breaking older clients or the metaserver is possible.
The metaserver does not need to be altered in any fashion.
Servers could send a port number as part of the info string, which typically includes the players and version. It would be prefixed by a colon, so multiport-aware clients could recognize and use the port information. Old clients would be unable to play on nonstandard port servers, but at least they won't break getting a list from the metaserver.
Thus you'd have a couple entries that looked like these:
foo.bar.com :16232 Number of players: 0 Version: 1.0.0 alpha
foo.bar.com :18346 Number of players: 0 Version: 0.7.2 alpha
Doesn't seem like it would be too horrific to implement
Multiple servers per machine solution
Multiple servers per machine solution
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