I would have thought a monk and barbarian would be the easier of the classes to add.
Agreed on Barbarian ...
But Monk seems tricky ... i mean how would you implement Deflect Misiles, or Slow Fall with curent reaction system? O_o
? Why would that be hard?
Slow Fall = Monk has feather fall as an active feature. Don't even bother making it a reaction, just a constant effect, whatever.
Deflect Missiles = two toggles, one to use a reaction to deflect/catch. And one to say if you catch a missile, then yes, you do want to spend a ki point to make a ranged attack. I guess the only difficulty here would be whether the system let you pick the ranged target or immediately picks the target for you by, for instance, throwing the arrow back at whoever shot it in the first place.