There are still a few users on old Windows 10 Technical Preview builds from 2014. In a few days, there won't be: their computers will refuse to boot. The affected builds that will completely brick themselves on April 30th are 9841, 9860, and 9879. You cannot accuse Microsoft of surprising users though, because Windows has been notifying them since April 2nd and force-rebooting every three hours since April 15th if they didn't take the warnings seriously. The current batch of builds are valid until October.
WinBeta has linked this policy to Microsoft's rumored piracy policy. My thoughts? No.
This is actually typical of Microsoft when it comes to pre-release operating systems. In fact, the only difference between this and Vista's pre-release (ex: “Beta 2”) expiration is that Microsoft relaxed the reboot time to three hours. It was two hours back in the Vista era but otherwise identical. That policy only applied to the previews then, and I see no reason to believe that it will be extended to released operating systems now.
Granted, with the Windows 10 continuous update structure, it does raise concern about what will happen if/when Microsoft releases a build that users don't want. For instance, imagine Microsoft decides to cut off legacy support for Win32 — will customers have the ability to opt-out of the upgrade treadmill and continue to use applications that are then unsupported, like practically every Steam game they own?
But I see no reason to think that this policy has anything to do with that.