As long as you have a legitimate copy of a Windows OS, there shouldn't be an issue. I, for example, upgraded from Windows Vista to Windows 7, which happened well after this "announcement". I have replaced several motherboards, and on the rare occasion Windows said "something is wrong here", I called Microsoft's automated line and had it resolved in minutes, with no money required.
But in that case you bought the upgrade, this is a " free " license upgrade, so you can upgrade now but if the motherboard goes in the future you will need a new license. I've done the same in the past with a windows XP upgrade. This time they're tying the s/n of your motherboard to the license.
Though it's possible they're not sure and covering their backs, but I wouldn't rely on it.
Ah, I see what you're saying, thanks to what
RevdKathy posted below:
Most of the info I've seen says this:
If something major happens to the device that requires something as monumental such as a motherboard change (basically turning it into a new computer), Windows 10 will require re-activation – which will require you to purchase a license. This is what Microsoft means when it says "life of the device." Additionally, you can't transfer a license to a new device. But, if something disastrous does happen, it's usually more cost-effective to just buy a replacement device anyway and that should come pre-loaded with Windows 10. However, if you happen to buy a new device with an older OS installed, you can get the free Windows 10 upgrade as long as it falls in the free upgrade offer period.
http://winsupersite.com/windows-10/how-windows-10-will-handle-clean-installs
Now, they've changed their minds on many things - a while ago they were saying there would not be an ISO for the upgrade, while the latest info is that if you do the upgrade they'll register your device, after which you can do a clean install. But 'new motherboard = new device' is their current position.
That is not good. Replacing a motherboard isn't creating a whole new computer, it's replacing a motherboard. Motherboards can, and do, fail. I don't like this aspect of the upgrade, and this is the first I've heard of it.
Hopefully, Microsoft will backtrack on it, because that is a terrible idea.