Never played a character built around the Shiv but I like your idea. Having both 10 AGI and CON and still be able to maximise attacks per round is someting unique indeed.
The only issue is being extremly dependant on critical hits which means dealing very little damage against creatures like bladelings but luckily there is Expose Weakness. Another thing is Shiv having not all that great critical hit chance. Together with 10 DEX and Recklessness it's only 20%. That's far from good. Survival Instincts is 30% but it kicks in when you're good as dead. To be effective you'd need to implement all critical chance you can get. Infused rathound leather armor can give you up to 15%. It's a long road until you can craft it but once you have it you're around 1 in 3 hits a critical.
Focus stim is 15% but it's situational so you'd have to craft lots of them.
Psychostatic Electricity also has a potential of another 15% but the problem is you need Premediation in order not to waste AP casting Electrokinesis so not only do you need 2 more free feat slots, you also need 6 INT. It can be done by leaving DEX at 9 and using the eel sandwich. The actual stack limit for Psy. Electricity is 5 so you could get up to 25% if you have two targets and you cast Electrokinesis on each. One is free and the other one costs 30 AP so you'd have 20 AP left but if you use Blitz and adrenaline you'll have 60 total allowing for 15 attacks - pretty good.
All in all if you maximise the critical chance potential (not including Survival Instincts) you would have a max chance of 75%. Survival Instincts would raise it over 100%. With Cheap Shots, Ripper and Critical Power, depending on enemy health Shiv can deal anything between 625% and 870% of damage. With 10 DEX the weapon damage at level 25 is 242% so the Shiv will deal 2 - 16 damage (depending on if damage is rounded or trucated). A critical will deliver between 12 - 100 and 17 - 139. If we include maximized Taste for Blood and Vile Weaponry the damage should pretty much double. This is only end game circumstances but overall not bad for a little piece of junk.
Like I mentioned it's very dependant on actually scoring a critical so I think that investing into Psychostatic Electricity might pay off, more than in any other build. With only 10 DEX the chance to hit against high dodge enemies are smaller than with 16 DEX so stunning enemies is even more important. I'd replace Fatal Throw with this feat because at 10 DEX a throwing knife costs 15 AP while refunding 18 - that's not even one extra melee hit. In order to get room for Premeditation, Opportunist would have to go too. Unfortunately because with all the Electrokinesis stuns it's great. Fancy Footwork is better than Sprint but it can't be taken at level 1 so it's required to take both Survivial Instinct and Thick Skull very early. Because of stat distribution as the last feat you have to take either Ripper or Blitz. Ripper is far superrior so Blitz gets the last call.
As a secondary weapon the unique glove Ripper would be best because sometimes you'd need to initiate bleeding by a weapon and as all other bleeding melee weapons have either 11 or 12 AP you want to make a bleeding wound and switch to shiv as fast as possible. Ripper does this very well - it's a 58% chance to make at least one bleeding wound. Taste for Blood is pretty late so it's not a priority weapon. Thanks to psi there is also some extra damage from Force Emission. My guess is that it's still inferior to a 16 DEX critical hits based monk but that one can't max both AGI and CON.
So this is how I'd progress the Shiv Assassin:
