They started development on Windows 7 a few years earlier than it was released though.... About 10 years ago... Had you read some of the comments, you'd have noticed this was already mentioned....
This isn't exactly news. Virtually every product made has a development stage. If you want to get into it, XP was designed years before it was released.
Historically, Vista was foisted off on the public as a paid product, when the reality of it was it was the Windows 7 beta.
This is SOP for M$. Every other Windows release is a fact finding issue. In the case of Windows 8, either there was a lot of muddled "group think" going on in Redmond, or they were trying to see how much they could get away with.
The whole "Windows 10 thing is free", is basically because the desktop market is shrinking, and you can't get away with charging even Windows corporate OEM prices, to have Windows put on a $50.00 tablet./So, Windows is now free but, it basically leads you to the M$ store where M$ is planning to recoup its losses. And, you now have the closed system paradigm, which is an Apple knockoff. Watching Apple's profits soar while M$'s much larger market share can't produce the same ROI, had to be pissing the Redmond boys of for close to a couple of decades now. So, if you can't beat them, join them.
If you have to talk to Cortana, then by all means, Win 10 is for you. The most stable copy of Windows, and the easiest on resources I have, is XP SP-2, on an 11 year old eMachines... Even Windows 7's controls are too restrictive for the environment I work in. No one has physical access to my computers. Hence passwords and UAC's are simply a PITA. I'll be damned if I'm going to tolerate some OS sending me to its store for apps, erstwhile it's logging my keystrokes, free or otherwise.
This thing with Windows 10 or nothing has already started with the new Intel boards. You have to download "Windows 7 installation kits", to get it installed. But, Win 8 & 10 go in without any additional effort.
You haven't come up with too convincing an argument for Windows 10, save for it's new and it's free, and we're pretty much fated to have it stuck up our a**es eventually. I choose to resent that, but I suppose you could chalk that up to me being a bitter old man.