Really it's mostly deciding on how the ranks will work, either player or character based, then deciding on how people progress in rank, either beating the player above them or by a point system. I'm a fan of the point system, and player based system, but it's a group decision.

Player ranks can be coded into the system I think to display under the names like statuses or bios, and would not require keeping track of win/losses of every character you use - something we can add to the characters ourselves. 

The point system was used on Hall of Records, and worked Well. It's simple but IN, I think raised a good point about just beating the top guy to advance. We could do it like the Seguleh in the Malazan series, but I don't know if you switch rank or just move one down. I imagine the latter. 

Another thing to consider is the judging, if any, for a ranked fight. That should be simple enough, however. As well as win methods and losses. Forfeit, death, surrender.