If ever there were a global stats tracker, a criteria would need to be established for "ranked" servers. Some non-cvar things you left out are: very restrictive or no admin access, dedicated connection, and maybe some restrictions on maps that could be included in the rotation.
These days there is quite a large disconnect between pub and match settings. There would probably need to be three types game modes to be ranked in: Clan Match, Classic Pub, Speed Pub. Each one of those modes would require a sub-set of cvar restrictions, maybe maps too. I'm not sure how different gametypes (dm, tdm, siege, pong..) would be dealt with either, but that's only a problem on pubs I suppose.
