I don't think Microsoft has a choice with regards to kernel access. Hell, individuals currently use undocumented NT APIs. I can't imagine what happens to backwards compat if kernel access is closed.
Apple's closed ecosystem is entirely different. They'll change architectures on a whim and users will go with the flow (myself included).
But Apple doesn’t have the industrial and commercial uses that Linux and Windows have. Where you can’t suddenly switch out to a new architecture without massive amounts of validation costs.
At my previous job they used to use Macs to control scientific instrumentation that needed a data acquisition card. Eventually most of the newer product lines moved over to Windows but one that was used in a validated FDA regulated environment stayed on the Mac. Over time supporting that got harder and harder: they managed through the PowerPC to Intel transition but eventually the Macs with PCIe slots went away. I think they looked at putting the PCIe card in a Thunderbolt enclosure. But the bigger problem is guaranteeing supply of a specific computer for a reasonable amount of time. Very difficult to do these days with Macs.
Good luck getting that through a regulated company’s Quality Management System or their legal department. Way too much business risk and the last thing you want is a yellow or red flag to an inspector who can stop ship on your product until all the recall and remediation is done.
See Satya Nadella has recently said that Microsoft will now put security above any other value at Microsoft. He specifically even singled out backwards compatibility.
Microsoft is a big boat. It takes a long time to turn if the captain orders it. But the captain has ordered it. I expect the sacrosanct nature of back compat to eventually die. Windows will never turn into the moving target that macOS is, but I expect a lot of old stuff to just stop working, when security concerns dictate they should be removed.
Apple's closed ecosystem is entirely different. They'll change architectures on a whim and users will go with the flow (myself included).