Having a list server that displays all jj2 servers under a constant version ID (regardless of the version used) is a bad idea. Remember that you cannot always successfully join a server when your version is different. Take 1.23 and 1.24 for example. If you were to use 1.23 to join a 1.24 server that hosts a TSF level/tileset then you would get an error.

If you're speaking of a common version (sort of as if suddenly all different jj2 versions would get magically replaced by a common version such as 1.25 worldwide) then yes, that would bring the community together. It would be nice, but impossible to achieve.

Still the best practical solution would be to use a kind of servers that can accept clients of any version and allow them to play a common game.