only 20W for 2GHz quad core A57 + 1Ghz 512 FP32 GFlops GPU on 20nm is very very impressive in my book. Saying that it consumes 20W without taking into account the very high sustained performance, is hiding half of the story. Because X1 efficiency is at the top of the market and it can be adapted to a tablet easily.
You asked
why Tegra X1 isn't likely to get a tablet design win and you got your answer.
No one accused TX1 of being inefficient. It's just not a proper chip for a tablet.
They could underclock and undervolt everything towards a 10W consumption, but then it might not even get far enough from the cheaper TK1 in gaming performance.
In a tablet, when it will be clocked lower and it will throttle to fit 10W envelop like everybody does, it will be suitable and still be miles ahead of anything QC has to offer.
You either did side-to-side, apples-to-apples comparisons on limiting power consumption to 10W on both chips using dedicated development boards yourself, or you own a magic crystal ball to be so sure of that.
Now is Nvidia pursuing this market, its the real question...
Like all Tegra chips before this one, nVidia is probably pursuing everything they can get their hands on.
The result so far is that nVidia could only find one device where to place TX1: their own set-top-box. And maybe a Shield 2, also from themselves.
The truth is that TX1 is a solution looking for a problem. The android games that are making money don't need high-performing GPUs. In fact, the number of android game releases with sophisticated 3D graphics is slowing down. Gameloft is going back to cheap movie tie-ins, EA's last demanding 3D game is the >2 year-old Real Racing 3 and they're now betting on bejeweled and plants vs. zombies, etc.
The F2P bubble didn't help either, because at the moment no one is willing to spend too much money on Android games that are always hit-and-miss.
Yes, nVidia is spending money on some exclusive PC ports. But the exclusive part is the problem. nVidia's greediness is clouding their ability to understand that, to enlarge the market and demand for such games, they'd need to let those games run in other SoCs.
nVidia will rather starve than let the competition take a bite from their investments. So they'll probably starve.