With all the, real, new Chromebooks coming out, there's also a surge in rumored ones. The Chromebook Pixel is most definitely a fake, though Google could be working on a more high-end device. However, it seems that there's also a Tegra 4-powered Chromebook in the works.
The Samsung Chromebook already uses an ARM processor, so a Tegra 4 in a Chromebook doesn't seem as far-fetched as it would have sounded a few months ago.
Google is already using Tegra 3 in its Nexus 7 and there's every indication that it will use the Tegra 4 in its second-generation Nexus 7 to be unveiled at Google I/O 2013 this May.
The Tegra 4 also promises to be a lot more powerful than the Samsung Exynos 5 used in the Samsung Chromebook. That's a good thing since the Exynos 5 is a bit too slow for Chrome OS.
All of this is speculation, all we know is that there is mention of an upcoming Chrome device in the Chrome OS source code, codenamed "puppy."
The code mentions support for T114 dalmore, the codename of the upcoming Tegra 4, which makes it very likely that there will be a Tegra 4-powered Chromebook.
It also makes sense financially, Chromebooks have started selling well recently, but only because of the price. In fact, the $249, €190 ARM-powered Samsung Chromebook started this trend.
Not only is an ARM Chromebook cheaper, it's also completely silent since it doesn't have any fans for cooling and uses very little power.
All in all, there are plenty of incentives to use an ARM processor in a Chromebook. And since the Tegra 4 promises to be the fastest ARM SoC for at least a few months, it makes sense to use it.
That said, a Nexus Chromebook powered by Tegra 4 to be unveiled at Google I/O alongside a new Nexus 7, possibly powered by the same SoC, doesn't seem too out of far-fetched.