No, no, no.
Iggy is hitting well right now, but literally one of every two balls he puts in play is going for a knock. That's insane, and literally impossible to sustain.
He's certainly proven that he can hit major league pitching, and his new approach is giving him huge improvement. He's driving the ball way, way more than he used to.
While he will never hit enough for a corner IF position, he has shown that he can be a .250/.315/.375 hitter, which is about an average SS, and with his glove would make him a well above average SS.
No, Iglesias will never push Middlebrooks out of 3B directly. BUT, if he plays well enough to push Bogaerts off SS (much like the Hardy/Machado situation), Middlebrooks could very well be pushed off of the position for Bogaerts.