I like the idea but I think a better idea would be to give Str based monks an increase in AB, something that many current monk players are no doubt very thirsty for. This way, you can have a different playstyle of monk that brings something different to the table and allows them to expand beyond being a flanker or a tank in the later portions of the levelling game.
I like this idea! A flat AB increase would be simplest. Maybe even a series of feats with escalating STR increases? Like so :
Feat name : Demon Fist Style
Requirement : Monk lvl 1, STR 13+
Description : You have honed your body into the deadliest of weapons. Your fists shatter anything you put your mind to. To you, the best defense is offense. You get an additional +1 to AB for unarmed attacks.
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Feat name : Dragon Fist Style
Requirement : Demon Fist Style, Monk lvl 8, STR 15+
Description : Your Ki empowers your natural strength, heightening your already impressive offensive capacities. Your +1 AB increases to +2.
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Feat name : Dread Fist Style
Requirement : Dragon Fist Style, Monk lvl 12, STR 17+
Description : You have become Dread, destroyer of bodies. Your fists are legion. Your punch is one of a kind. The +2 bonus becomes +4.