I was very excited about Pixate when I followed your link, but after the initial excitement it turned out that it's one of those stupid MVP (potentially) vaporwares that's just a cute landing page with a form for "give us your email so we can let you know when it's available" in the signup/download link... It's a concept, not a product. And for all we know, it could take a year or two before it's released. Yet, the landing page makes you believe you can use it today:

"Long gone are the days of tedious image slicing [..]. With Pixate, designers and developers alike can conceive, [..]. etc., etc."

I really hate such "tricks". If it's a concept, just say so in the landing page - we won't kill you! We will find out in the end - it's hardly a secret, and will be pissed when we click "Download SDK Now!" and find out it's in the early stages of development...

I might've been interested in backing them up on KickStarter, but I really don't trust them now (because of this trick they pulled on me). What if their framework has a serious bug (a severe memory leak)? Can I trust these guys to tell me so if I build my (imaginary) $50,000 app using their framework? No, I don't feel that confident.

As someone who backed them on kickstarter I probably have a biased perspective, but it seems to me that the product is coming along very nicely. They are quite open to with the development of Pixate to backers. There is also a Pixate demo app on the app store to see how it works on a device. Pity they haven't been so open with nonbackers.

I would be very interested to know how this compares to Pixate.

Pixate appears to be a large project and very ambitious, so I am surprised to see NUI appear, seemingly out of nowhere.

No surprise, any good/successful idea is always copied.