To me there are a few issues with windwalkers currently in PvE and PvP. As far add PvE lack of cleave, over priced interrupt, no execute and terrible mastery. For PvP lack of burst/ hard hitting abilities.
Here are my suggestions to fix these issues:
Interrupt: glyph, remove the silence lower the cost to 15 energy to align it with rogues/feral.
Mastery/cleave: change the mastery to not only proc a free blackout kick or tiger palm, but also have it hit 50% harder against a single target(obviously would have to be balanced, this could also scale with mastery)if only one is in range or hit a second target if there is a second target in range.
Execute: RSK damage boost increased to 25% when applied to a target in execute range. Giving us a 10% damage increase in execute range which seems relatively in line with other classes.
The mastery and execute changes would also increase our burst and finishing ability in PvP which is really what we are lacking.