T.E.A.M.F.O.R.T.R.E.S.S.2.

We all know the game "S.T.A.L.K.E.R."
This game has different kind of patch-system.
You can see the number of your current game's version. And you can play on the servers with the number equal to yours. Example: your ver.1.5.0.05, servers are - 1.4.0.61, 1.4.5.23, 1.5.0.05, 1.7.2.34, etc.
Different version of the client (and server) means that you're agree to play with/without known(fixed by patch) bugs. So, there is an option to play the lower version game.
Now imagine this... ok, now pause: I was speaking about linear style of the updates STALKER uses. Now imagine, that you can mix patches, and you have "N-dimensional" update-system. You can choose bugs to be fixed in your version and your server.
Now imagine this in TF2. You choose bugs fixed (by ALL known updates) and any bugs not-fixed (if there is compatibility between those bugs/glitches). Then you start search for the servers with the EXACT version of the choice you did. Or you can search for all servers and then choose the one you want to play on (also, your search could ignore servers with the different - than the most patched version is - version of the game). As you understand, there would be no (death)matches between players with different version of the game.

I hope it'll be done one day...