IIRC, Theymos has hinted about adding at least one new rank, and members have chipped in with suggestions for name and customization,big however this should happen, then besides an activity count there would also be a new merit requirement that one should reach to attain this new rank.

Also, I cannot think of any motivation to add other ranks available for purchase, the admin has said that the forum does not need extra funds and copper membership pretty much covers the necessities that one would need when joining the forum and if they need to advertise a little service.