Not sure about the GP, but I interpreted it as being about Microsoft moving to a subscription service, which Windows doesn't fit into. The sentence was:
Which is where Windows is now. Windows is declining, and as Microsoft moves to the subscription model, will die even faster.
That's the exact opposite of him saying "Windows is switching to a subscription model". He's saying "Windows will die, because Microsoft is moving to a subscription model". If he was arguing Windows was switching to a subscription model, he wouldn't be arguing Windows will die as a result of Microsoft moving to one, would he?
I would be interested in his reasons, but I suspect the logic is something related to the cross platform nature of most cloud hosted offerings, which Office 365 is an example of. If you can use Office on a ChromeBook, you have less need to use Windows. And if you're trying to make money by selling subscriptions, ensuring everyone has 24/7 access regardless of device is probably a good idea and a major selling point.