I was thinking about repetitive uses of Feint the other day. This was occasioned by me totally catching someone flat-footed with a good feint, but then seeing him clue into my feints.*
A cumulative feint penalty makes sense, much as the same way as the cumulative bonus to defend against repetitive moves does.
This admittedly assumes that your feints more-or-less resemble each other.
It's not enough that your opponent knows you like to Feint - overly-examining incoming strikes as if they were feints is effectively the same as falling for them, in my experience. Also, just knowing it might get used doesn't mean you recognize them when they do.
Still, it can get boring in a "climactic" duel where both the NPC and PC generally just use Feint until someone rolls really well. Cumulative penalties mean you really have to consider when to launch it, not just fire one off every turn in the hope of a good roll by you and a bad one by your opponent.
Fool Me Once. Repetitive uses of Feint against the same target are less and less effective. Each Feint past the first in a given engagement is at a cumulative +1 in the Quick Contest for the defender.
Alternatively, Ruses suffer a penalty of +2 for the defender for each one - it's much harder to keep saying, "Hey, look over there!" with any real effect. Beats would be unpenalized - they're not subtle tricks, they are physically forcing you out of position. Knowing they are coming doesn't help very much!
I toyed with the idea of +2 (and +4 for Ruses) but I didn't go for it because it seems a little on the high side.
I haven't tried this, but it's an interesting idea. It might make sense to bust it out only when it's a very particular combat, say a duel or a fight with a boss villain.
* Basically, SHOOTO as taught where I trained uses a step-feint that is identical to the step-jab except for the part where the jab doesn't launch. I did that and immediately launched a cross and caught my sparring partner wide open as he reacted to a jab that wasn't coming, before he could cover the straight. Had I actually just did the usual 1-2, the straight would have been a bit delayed and he'd probably have been able to cover it.