I don't see the logic in that. If it's selling so poorly because it's old technology, what's the point of holding out? Why wouldn't they release a new model that would sell more?
Your presumption that the nMP hasn't sold anywhere near as well as the cMP 5.1 is interesting. Curious why you think that?
Well if they had a certain target projection of how well the nMP will be doing, which according to my conceived speculation derailed and wasn't nearly en par with the estimations (because not everybody was wowed by their revolutionary design solution), then the only logical business related thing to do is to extend its lifetime and try to make as much profit of it as possible right before the public gets really pissed and asks where the next update is, which in my opinion is what's happening right now.
Or how do you explain that lanky chasm of silence right after a complete redesign within todays's fast moving computer market? Because Apple is waiting for new intel chips / thunderbolt 3? Apple's updates have never been "technology" related, where in a sense they would've waited out for something particular they wanted to integrate, people speculate on right now.