I've been thinking about the same thing, and I have a couple of non-playtested martial arts styles I can share. I don't even have Martial Law yet, so I've only been able to compare these to the couple of styles in the Core book, so I'd be happy to have these critiqued for balance.
Falling Boulders Style (St): emulates the unstoppable avalanche. Practitioners gain +10 to OB when attacking with no parry to DB, and gain a +10 to maneuver checks for knockdowns attempts.
Flowing Water Style (Ag): imitates the yielding nature of water. Practitioners add their Insight bonus (if positive) to DB against melee attacks when attacking with this style, and make subdual attacks with a -10 modifier to the attack roll instead of the usual -20.
Surgeon's Knife Style (Ag): a short sword weapon kata that especially targets the opponents veins; any bleeding results on the critical table are increased by 1 point per round.
Again, I'm not sure if some of these are overpowered, or if they actually ought to scale up more. Especially flowing water, should that be an additional Insight bonus to DB at every 10 full ranks?