Hypothetical Microsoft/Linux scenario question.

This is obviously a hypothetical question.

It's obvious that Microsoft wants everyone who uses older versions of Windows switched over to Windows 10.  Now if Microsoft took some sort of drastic step to make updating to Windows 10 basically mandatory, like announcing that they will no longer provide any more security updates for older versions or some other announcement.  Would that translate into Linux getting many, many new users and finally becoming mainstream for desktop users or would people, including the ones that claim to not want Windows 10 and will use Windows 7 till support ends, just switch over to Windows 10 and accept the switch?

If the answer to the question above is that nearly every one would just switch to Windows 10, then why doesn't Microsoft just enact a deadline for a mandatory update and just get it over with?  Didn't Microsoft stop supporting windows 8 shortly after 8.1 was released?  So why not just say that they will no long support older versions and that 10 is the only version they are focusing on?