For various reasons, I run multiple OS's. I was part of the recent wave of upgrades to WIN-10 because I have to anticipate what my accounting clients are going to run into when they upgrade which they tend to do without warning.
I personally think MS is just assuming that people will run through the process without thinking much about privacy settings and security issues on the other side. I'm a wee bit OCD about that, but the public I try to work with isn't even when they're told to be careful. I'm still baffled by the number of systems I deal with that have either no antivirus or outdated versions, no firewall, etc. Let's face it, if MS gains marketing data in exchange for a "free" upgrade, most folks won't complain. What I'm also concerned about from a practical manner is the fact that various support builds are going to be pushed though without the option of deciding when to install meaning that various drivers that worked earlier are suddenly off in the ozone upon restart.
There is also the matter of when, where, and how MS will acknowledge problems with the OS. For example, the Edge browser seems to have some real issues integrating with printing which simply aren't there when you switch back to IE-11 which fortunately hasn't been removed (yet), but only disappears from view.
MS's view of the future which they've been fairly clear about is a device-spanning OS that they're going to drive and I think that's one of the main things to keep in mind with WIN-10.