Ranger REG said:
I wonder if there are any further exchange of class abilities for martial arts feat between levels 21-30 and beyond, for the OA monks.
The abilities a monk can trade in according to OA are: Stunning Attack, Deflect Arrows and Improved Trip. These are all specific abilities, and rather close to the effects of various feats (though Stunning Attack is better than the Stunning Fist feat). They are also all "boolean" abilities - you either have them or you don't. You can't trade in the monk's Slow Fall, increased unarmed damage, AC improvement, and stuff like that - just those three, discrete abilities.
At level 21+, the monk only improves in "gradual" abilities: AC, Speed, and various things that use the class level to calculate something. None of these abilities should be tradable - they're just "doing stuff better", not "doing new stuff". In addition, they get epic feats every now and then (levels evenly divisible by 5) - that's what provides the customization for the monk.
BTW, I'm working from the playtest Epic rules here (haven't been able to afford the ELH yet, not to mention that it hasn't arrived at my LGS), so I might be mistaken about what monks actually get at level 21+. If so, oops.