implementing an ath system in an fps isnt hard, if you run you lose some, if you hold your breath you lose some.
but you think you could but this in a melee game, i know you can find this in age of chivalry but that game has basic combat system. but in crpg, with hold attacks, feintspamming, spamming, blocking, double blocking against hilstslash or fail footwork, chambering, backpeddaling, jumping, kicking? how the hell would you implement it for all of thesse moves? how will you implement it without ruining everything?
this idea is fail but makes many people fantasies