DP does not need a ranking system. First of all when the good players want to play, someone gets a pickup game and tells people on IRC. If you had a server where only certain skill level people could join, you're not going to have a very populated server.
Public servers are pretty much the place for newbs to get better, and good players to mess around. I'm sure newbs don't want to see they have a .63 KDR. Most of the good players that pub just mess around (PGP, jump around, etc) I think it would just be pointless to spend time on a ranking system right now when there is so much other stuff that could be done.
And y00tz, are you serious about letting people choose their own skill level? All the newbs would rank themselves the highest rank(except for the occasional honest player like you or m7). Also a good player could just lower their skill level then go into some server and go like 40-2.