It's fair enough for MS to 'let users know' and for me, it would very much depend on how this works. I guess it's what is implied by "nag" screen.
If it brings up a suitably worded warning once, and requires people to acknowledge EOS and the implications ..... fair enough. Consider me duly warned, and thanks for letting me know.
But then, I shouldn't need to start messing witb reg keys, or whatever, to stop it recurring, because just clicking "I know, now go away" would suffice. Nor would I categorise such a warning as a "nag".
That word rather implies that it'll keep nagging until it detects that you're upgraded. And if it does that then I would find it objectionable ... if MS could get at my W7 machines to install it in the first place which, unless they installed ig quite some yearx ago, they can't.