Over on the SJG forums we've been having a discussion on counterattack, which spun into discussions of Riposte. It's here if you want to read it all.
Out of that discussion I got an idea. This is totally untested, but doesn't seem prima facie broken. Basically, ditch Riposte. Replace it with Deceptive Parry, from the GURPS Martial Arts Designers' Notes.
Fixed Level Riposte. Remove the Riposte mechanic from GURPS Martial Arts. Replace it with Deceptive Parry, from the designer's notes. (Short version: Parry at -4, opponent's defenses are at -4). Deceptive Parry becomes a Combat Option, not a technique, and cannot be purchased or improved.
You can combine this with:
Fixed Level Deceptive Attack. Deceptive Attack is now a flat-cost option. A Deceptive Attack is -4 to your skill in return for -2 to your opponent's Active Defenses against that attack. All other rules apply normally - you can't reduce your final effective skill below 10, you can't combine it with certain other attacks.
This turns DA into a mirror of Telegraphic Attack, and simplifies the choices available. Either you do it or you don't.
If you wanted to do this to Setup Attacks, too, it's easy enough - -4 now for -2 later, other rules options as selected from Doug's article.
It's debatable if you'd need Counterattack (also from Martial Arts) or not. I'd say yes since it fills a niche (Obvious Attack vs. Sneaky Attack, Risky Parry based techniques vs. Risky Attack based techniques). You could always cap it at between default-1 and default-3 if you want it to be harder than a normal attack, but I don't personally think that's necessary.
Pros: This would simplify riposte, since it's a -4 all the time. If you allow Deceptive Parry to be learned as a technique (it's original intent), you might want to consider Gnome's suggestion. That limits your improvement to default-2, so you can get better at it but not by so much it's always better than a normal parry.
Cons: Less options for the highly skilled. Makes for very fixed options in combat instead of true ability to leverage skill. Untested.