Actually something similar was done in Pathfinder for monks. Their basic class feature, Stunning Fist gets improved with levels. Monk can choose to instead of stunning for 1 round apply different effects for more rounds. At high levels they can even Paralyze.
Also if the unarmed strike is going to be the only weapon to use, I suggest giving monks full BAB with Flurry (again like pathfinder).
Also Since the monk needs amulet of might fist and bracers of armor to survive and the game does not support Wonderous Items with multiple effects Monks will sorely lack magic items slots which will make them almost useless at high levels. So I suggest letting monks equip their Might Fists in their weapon slot (call it wraps) so they can still have the neck empty for Con and bracers empty for Dex or Bracers of Armor.