This is the same way that SafetyNet killed alternative ROMs on Android.
>viable Windows alternative
Coffee just shot across my desk reading this. You are too deep in a bubble to realize that to 99.7% of people desktop Linux is an "obscure hobby OS", on the off chance they even know what it is.
You're talking about the popularity of Linux as an alternative, I'm talking about its viability. It's viable because it runs web browsers just as well as Windows and that's all the average user cares about.
Regardless, the point is that any alternative, Linux or not, will be dead in the water once WEI rolls out. Doesn't matter how good your OS is, if it can't access the mainstream web it will die in obscurity. The same way that Windows on phones died because it couldn't get all the useful apps.