Doesn't look bad actually.
Crippling Strike was maybe not the best choice as Kukri does the same thing, even better. As you've noticed it is the best support knife for most of the time as you can stack max cripple debuffs very quickly. That feat is still not wasted however. You could replace the Kukri with the unique Humanizer knife when you get it. Awesome for CC.
Since you're going for high DEX it would be good to get Fatal Throw asap. Throwing knifes are considered light weapons so the base 18 AP cost gets reduced by 4% for each DEX above 5, meaning when you kill with it you get way more AP back then you invest in throwing it. It has also perfect synergy with Ripper. Other feats you should fit in: Critical Power, Blitz, Expose Weakness and Cut Throat. Since you already have 6 INT I assume you want some crafting feats and you should definatelly be able to put lots of points into tailoring. As for the feats Power Management for stronger shield and Skinner would be good choices. Maybe Weaponsmith if you can squeeze it in but there are usually more important feats like Nimble for example. Interloper is also a very good choice if you have trouble closing in for the Cut Throat kill.
See, this is the problem with aassassin builds - there are so many good feats you can benefit alot from but so few feat slots. That's why I actually prefer not to pick crafting feats and leave INT at 5.
One route is to go for max AGI, as you did, the other to keep it at 6, DEX at 14 (You can still get 4AP attacks with Taste for Blood. 5 WIL as well for Ripper, leave INT at 5 for Expose Weakness and Cheapshots and maximise CON, not only for Thick Skull but also for Survival Instincts later on as critical chance and damage is your bread and butter.
It looks something like this:
