Yeah, I feel like a lot of people misinterpreted the end of IM3. Blowing up the suits, removing the shrapnel... that wasn't "I'm done with being Iron Man."
He built all of those suits because he nearly died at the end of The Avengers. He had PTSD, and compensated by building a ton of suits ready to handle every possible situation that could arise. He felt vulnerable, and echoed what Cap said; that he's just a guy in a suit. But after the story arc of Iron Man 3, and showing that he can be a hero with or without the suits, blowing them up at the end was a symbolic gesture to display that he'd overcome the fears that had driven him to build them in the first place.
So really in AoU, he had the MK43, and I assume the MK45 was just in design phases as "the eventual next step", because that's what Tony does. Hes always improving. I don't think the MK44 necessarily counts in this regard because that was a specialty suit that it sounds like Bruce requested/participated in, rather than Tony just building a new stockpile of suits.
With that said, while I don't think the MK45 was a "showstopper," or got a whole lot of the spotlight, I really like the smooth, streamlined design, and will happily purchase a HT release.