They are really getting desperate to get this garbage on as many computers as they can!!
Trying to make other OS's not work in an attempt to force ppl to Win 10!!
If M$ made a mistake, it was failing to promote the "upgrade" as a fully-activated "clean install" or clean-install in a dual-boot Win7/Win10 system. They were pitching the "upgrade" to mainstreamers and people who don't want to fiddle with OS conversions the hard way.
But the dual-boot capability and simplicity of creating it was always there since last year's release.
A clean install of Windows 10 -- as some VHD overlay, as a separate partition and volume on the same boot-system disk, or as a separate partition and volume on a second SSD/HDD -- will only rob your existing system of (initially) 20GB plus desirable free space on the target volume.
Once the Windows 10 installation has been activated on the chosen hardware platform, you can remove it, reinstall it later (after the deadline), and reactivate it effortlessly.
Failing to do it now means that you'd have to pay for it later, while creating a dual-boot system now means that you can play with the new OS and tweak it to your pleasure over some leisurely period of time while you do your regular business with Windows 7.
With any new Windows OS, I'd noticed that even a clean installation results in some Windows "red-bang" events in the Event Logs that require some investigation and solution-tweaks. I suspect that a grand roll-up "service pack" as rumored to occur after July for Windows 10 may eliminate some few of those events.
But a dual-boot system also means that I can trouble-shoot those errors and take my time about it.
With my laptop, I had replaced the DELL branded-Win-7 with a regular white-box OEM license. So both Win 7 and Win 10 installations have an equal "lack-of-bloat." And it seems to me that Win 10 is faster and "snappier" than Win 7.
With clean Windows 10 installation dual-booting with a "mature" Win 7, you can also install your software at a leisurely pace, and those licenses will also reactivate without problem for that particular hardware. But most of those licenses -- like Office 2007 through 2010 or 2012 -- can be moved from one machine to the other.