-If you make global rank based on wins, then it can still be bypassed with wins on whatever mod (jousting, problematic).
-Qi can be bought so that renders the qi system quite useless, aside from the fact that it's easily farmed.

If you insist ranking, then it should take place in so called 'official' mods (aikido,wushu and so on) - the rest doesn't take place in statistics, at all. Private rooms enable you nothing. This means we'll have to categorize which mods will be taken seriously and which mods are crap/useless. I think someone already mentioned this, idk.

With all the fresh points given, i still stand by my suggestion: remove the ranking system. Because of the amounts of mods here and this game in particular, there will always be a way to undermine any modifications you might make, and you'll still only have a half-decent system, which won't be enough (do it right or not at all). As far as the 'rank farmers' are concerned, they'll also find a way to farm their mod rank in private rooms. Better to crush all hope and be done with it. I might have overlooked on some details here, sorry if i did.