Ganking isn't really class tied. A fighter ganks because his potions last less than ten minutes, which is a rather small window to do any kind of meaningful, atmospheric roleplay within. A caster with spells that last for 1-2 hours or more ganks because it's ideal and optimal to kill someone with an attack spell or two that they probably can't escape from.
Anyway, as far as the feat itself goes, there are very few that give AB at all, and if you could grab this on a 3/4 or 1/2 AB character multiclassing into fighter, it would be in extremely high demand. I don't know if fighters need quite that much AB though, and if you want to bank everything on one attack battojutsu style, there's a class with an action ability for that.
I think mappinger is on the right path here, if the damage of dirty fighting scaled up a bit more or something, you might see people use it more, but we have power attack for that and it has a relevant drawback.
A feat where a character becomes a master of dirty fighting techniques should be similar to sneak attacks where you deal more damage to enemies that are knocked down or blinded or something to that effect. Something properly dishonourable, not just first-strike supremacy.