While a somewhat valiant effort from a specs/control perspective, I think this is going to be a pretty big flop. Primarily because it doesn't have much of a market, which means that they won't be able to overcome the chicken-and-egg issue.
There's a reason why the main gaming console manufacturers also have large development studios as well. Every new gaming device needs a killer app to launch it past the critical mass where it becomes economically beneficial for outside developers (3rd parties) to also release software for said platform.
nVidia doesn't have game studios (that they've announced anyway) so they're going to be relying on the broader Android gaming developers. However, Android developers are going to be targeting the hundreds of millions of phone/tablet Android devices and not unknown number of Shield owners.
So if very few developers are going to take the development resources to make games that take advantage of the Shield then how many gamers are going to want to spend the kind of money this will cost, when there are MANY other great alternatives (E3 this year will see the announcement of PS4 and the next Xbox).
If the hardcore gamers aren't going to be purchasing this system, then that leaves the so-called casual gamers. However, by definition this thing is targeting hardcore gamers so it doesn't have much appeal to casual gamers at all. Which means there's a very narrow market segment that is seriously interested in this.