Currently Shintao vs Ninja Spy (even without the shortsword part) is weak, not to mention the extra junk feat required. If Shintao monk gets automatic longsword proficiency and centeredness at Shintao I, and gets improved critical, longsword at shintao II, this can make shintao worth taking.
And just to balance out monks who wants to use longsword and not shintao PrE, remove the weapon focus, slashing from the requirement of whirling steel strike feat, and make the feat selectable as monk bonus feat at level 1/2/6