The old method of changing the default shell still works. Although I don't think you replace/move explorer.exe anymore, but just change registry keys. When used in embedded systems or kiosks, this type of functionality is commonly needed, so it is unlikely to change.
When I talked about things changing, it was more regarding changes that:
- Improve security and stability by disallowing software from invading other address spaces to do patching.
- Prevent modification of the operating system itself, by more thoroughly enforcing signature checking, file integrity, and with periodic large system updates that are effectively like full Windows version upgrades.
These improvements may make Windows more secure and stable for users, but combined with modern PCs that come with Secure Boot enabled by default (and unfortunately, some that came with Secure Boot forcibly enabled during the Windows 8 era,) it makes modifications and customizations more challenging.
There's no clean mechanism for which a piece of software like WindowBlinds can exist, and indeed, sometimes running Stardock software in modern Windows can be troublesome. A while back I hit a bug in WindowFX that effectively bricked your Windows install if you were running with Hyper-V enabled. It was fixed by Stardock but nonetheless, with a living OS like Windows 10, breaks like this can happen more often, without warning, and there's still not good alternatives for lots of customization stuff.
It's interesting because there are actually still lots of ways in which Windows lets software extend the operating system - probably more than any other operating system, but most of them are very old and not very reliable/stable.