Maybe, but...
Unless Microsoft goes the way of locking their system down to absolutely prevent any apps from being installed from any source other than the Appstoreit still isn't the death knell. Third party developers and development houses won't stand for it and if MS has 2 brain cells left to rub together then they aren't going to go out of their way to piss off them off. Microsoft got to where it is today by providing a platform which everyone else was allowed to build on without having to go through them to publish their software. Burn that bridge and we may actually see the "Year of Linux."