Is this sort of thing still going on these days? Is it even possible with W10?
It's still definitely doable on Windows 10, but a little bit harder. For example, enumerating open windows is little bit more complex now due to the nested way Windows reports them. Also, a fair amount of what you'd think would be part of explorer.exe (as the desktop) now run as their own apps - you have to disable them as well so as not get conflicts with your replacements.
But in short, any replacement shell written in the XP/7 era will probably not work that well under Windows 10 due to the under-the-bonnet changes.
For non Windows people:
In the Windows registry there is an attribute that defines the 'shell' that loads after you login. By default it's explorer.exe. Explorer.exe looks to see if it's the only copy running, and runs in 'desktop mode' - creating the taskbar, putting icons on the desktop, and reacting to system-wide keypresses and mouse clicks. Because MS called the registry attribute 'shell' this is what Windows Devs call the 'desktop'. By contrast the command line prompt is referred to (incorrectly) as the console.
Launching further copies explorer.exe results in only the File Browser part of it appearing.
I have since moved to the new Windows Terminal Preview.