The more I think this over...
The more convinced I'm becoming that you might actually want to prefer buying your Win10 version in a few years instead of relying on Microsoft's "freebie shove down the throat" approach. Sounds crazy?
A freebie is more or less just that: even if they change the whole thing upside down then you really got no means to complain or get any protection against it because... Yups: it was free, it's "as is" and as such you more or less agreed to whatever brilliant ideas Microsoft has in store for you.
Now... I'm not claiming that buying is the ultimate solution to this. Worse: it even depends on the country you're from (even in our "united" Europe the laws on this still differ per country). Even so: you'll have (a little) more protection against "we'll change this because we can" for the simple reason that you bought something, and under national law you'll be protected against scamming and fraud and such. You'll also have this "reasonable expectation" rule (depending on country).
So for starters I expect Microsoft to be a whole lot more transparent with the commercial versions of Windows 10 vs. the freebie versions. They'll have to: they can't just sell you "trust us, you'll like it". Not only is that illegal, who would buy that? So I'm expecting to see exactly what features will be provided, what caveats we'll have to cope with and which features will be external (or added through 3rd party stuff, such as the Microsoft store).
All in all I think it'll be much safer to wait for this to happen. It'll cost you money, but at least they'll have to deliver what you're paying them for.