Why not supporting newer VMware updates within the same version, while Microsoft is doing the same with Windows 2016 and it's large Anual updates and here HPE doesn't look behind the "DOT" for the version number.
Windows 2016 as of may 2019 is completely different as Windows 2016 from early 2017, but this IS supported while obviously no testing takes place in these cases as well? How can you garantee data integrity if, as I may quote your own words " HPE will no longer test and qualify newer OS versions or configurations."?
Why is this different than the VMware situation? Your clients don't ask for ESXi. 6.7 to be supported, they only want their 6.5 versions to be supported so they can remain secure and don't have to complete a jigsaw puzzle each time an update is introduced for their Gen9 Proliant servers.
Now they might be confronted with a "NO Supported configuration" notification if they call support if a minor VMware update forced the U2 installation in the background.
Otherwise introduce a fancy upgrade program and let MSAx04x users upgrade to an MSAx05x version for a reasonable price!