It will have most if not all the compromises of an AIO.
I have to agree, seeing what MS rolled out with their other Surface products, it mimics apple in the sense that they're sealed and non-upgradable.
Why would any of us switch to Windows? If I were to guess it would be for a more powerful, less expensive, upgradable machine.
The Surface line is not that much less expensive then the Mac line, but it has been historocally more powerful then the Mac line. Some of the models however have been more expensive, i.e., paying nearly 2k for a 13" dGPU equipped laptop vs. Apple's 13" MBP.
Maybe if you you MUST HAVE an AIO then it will be a solution for you but aside from that...I don't see this affecting many of us too much.
I love the idea of the AIO, and I've long grown out of the idea of building/upgrading my own machines. I did that for years, heck, I used to sell/repair computers back in the day, so I know my way around PCs, but at this point in my life, the AIO fits my needs. The iMac that I got last year has been the best computer I've owned. Even now, nearly a year later, its been great and I have zero regrets.
I think many of us in the iMac forum, love the AIO design for one reason or another, so I can see the allure of the Microsoft product. I think Apple has gotten complacent, and while the 5k iMac is awesome, there's so much more they can do with it. The MBP probably highlights Apple's complacency more, but the fact remains Apple needs to step up their game or risk further sales.
As for MS, the Surface Book I bought has been a great purchase, but I do wonder about a desktop, given the market's contraction.