I'm of the mind that Win10 is at best a lateral shift from 8.1. Though I suppose that's somewhat off-topic.
At this rate it would not surprise me if an automatic update would forcibly update to Windows 10 with no way to cancel it at all.
Their approach with KB3035583, the "Get Windows 10" program update, is incredibly sneaky and I would almost suggest malicious, even. Hiding an update will hide all future versions of that update, unless the new one is marked appropriately, in which case, it will appear again. Microsoft has released every new version of the GWX update with that mark; so any user who had hidden the update, will see it again and it will be automatically selected as well. This seems rather user-hostile; if a user, such as myself, has hidden the Get Windows 10 program, then it is not reasonable that any change to that program would change that, as it is the specific purpose of the program- upgrading to Windows 10- that I do not want to have performed on my systems.
The presence of advertisements within Windows 10 seems to partly explain why they want to get people onto Windows 10 so badly, considering that in terms of features it is rather lacking. (and usable features, moreso, do NOT get me started on VPN connections...) But besides displaying advertisements, there is also all that sweet, sweet information they will be gathering about how users use their PCs, what programs they run, for how long, etc. I'm sure there are a lot of interested third parties that would pay for that information. This may be why the Windows 10 EULA explicitly gives Microsoft sole proprietorship over the gathered information- "By accepting this agreement and using the software you agree that Microsoft may collect, use, and disclose the information"
EDIT: This is not conspiracy theory stuff here really, as there are certainly loads of perfectly legitimate uses for the gathered information to make various products better, the main concern here (IMO) is that individual users should be able to, at least, opt out of that collection if they desire.