The NUC is not really for the same space - it's a desktop/server thing, totally unsuitable for embedded.
It's really a shame. I don't think Intel needs to lose the low end - they have the technology, but lack the will. Their mobile parts would work fine on an RPi-class board and the architecture would be far more cohesive.
It may not be in exactly the same space, but it has the same problem. It's way overpriced for what it offers. I still don't understand why they cost more than a full tower PC with better specs. It's not like they're some crazy special hardware.
The real problem here is that embedded is a too broad term most of the time as it defines a specific way of using a computer, not its capabilities, size or power constraints, etc. You can put a desktop tower into a vending machine and still call it embedded (and if its a big machine it may actually be an OK solution).
I chose embedded systems as my specialization during my CS degree. We spent a week in one class just trying to define what exactly an embedded computer is.
Your definition is pretty much what we came up with--they're defined in terms of use. But at the end of the day it's one of those "I know it when I see it" things.
It's really a shame. I don't think Intel needs to lose the low end - they have the technology, but lack the will. Their mobile parts would work fine on an RPi-class board and the architecture would be far more cohesive.