As I've discovered, there is a limitation of the Mac that does interfere with the ability to run some newer operating systems - UEFI. The UEFI 2.0 specification was released on January 31st, 2006, but Apple computers continued to use the outdated UEFI 1.1 specification through until sometime in 2014.
When Microsoft introduced UEFI boot compatibility into their operating systems with Windows 7, it was assumed that any computer booting into Windows on UEFI would support the UEFI 2.0 specification. This was true, with the exception of the Mac. Hence why Boot Camp starts the computer into a BIOS mode emulation state in order to boot Windows.
If you attempt to boot Windows in UEFI mode on a Mac, chances are you will encounter problems. For me, I noticed that Windows was unable to correctly write to Serial-ATA attached devices, and would copy the Windows installation files but fail to update the boot configuration data, rendering Windows un-bootable. When I imaged the Windows install from another supported machine and placed it onto my MacBook Pro (15-inch Mid 2012), Windows would start to boot, but would lose video soon after because Windows and the NVIDIA drivers were expecting some 2.0-specific calls in the UEFI firmware to be present.
So, correct, Microsoft will continue to support these machines for years to come, or at least as long as BIOS support is still included. When the industry starts introducing OSes with UEFI-only boot support, then the process of making those operating systems run on our Macs will become a lot harder.
Not that I intend to let that defeat me. I'll install a Linux distro on that machine if I have to.