You don't need to gauge interest if you believe in the product. The story they are selling of a truly immersive environment is something core gamers have been looking for for years, and there is a pretty full graveyard of companies that tried and failed to reach that holy grail.
There is no reason to look to a Kickstarter in order to prove some point that there is consumer demand for it. There absolutely is, and this Kickstarter is pretty much certain to succeed. Which, again, leads me to think that something is going unsaid.
> "...this Kickstarter is pretty much certain to succeed"
They why not do it? Honestly, I cannot understand the viewpoint you seem to hold. This is a massively easy way to get a lot of attention, early money and get developers thinking about what to do.
Do you really believe all those folks in the video would risk their reputations by putting their name to it without believing it? I bet there are ton of folks at Valve right now who've pledged. Are they wrong to do so?
In any case, I trust John Carmack on this one. He's demonstrated tremendous personal integrity again and again.