Although the infiniteresponse website is a little bit vague, the VAX-77 does not look like a hoax. The company appeared at the South By Southwest music conference in the U.S. this year and there's some video footage of somebody unpacking and unfolding one of these keyboards (http://speakerdesignstudio.com/portable.html) - though this footage doesn't appear on the official website, and so it may not be a completely accurate picture of how it works.
Not only is this keyboard lighter and more compact than other 76-key controllers, but also it's supposed to be really sturdy, with a chassis that has been made of strong, light metal instead of plastic. It looks like a good option for the travelling muso.
I'm mostly interested in the keyboard action, which is very fast and evenly weighted, according to the infiniteresponse site. Apparently the keyboard is responsive to the "slightest key movement". It would be very interesting to see exactly how it compares to standard weighted controllers like my Fatar VMK-188. The keyboard's action would probably be the most important factor in judging how good it is as a match for Pianoteq. If the action gives you better expressive control, then it will probably be a better match, unless you definitely need that extra octave of course :)
This keyboard could be really exciting... but you can bet your bottom dollar that it won't come cheap. I might be saving up for a long time if and when it is released.