@SASS S Is it possible to boot the Raspbian Stretch Desktop into readonly memory.
Yes - look into booting and running from a RAMDisk. I don't see where anyone has done this because Linux takes a bit more memory than WinCE and doesn't leave much for your application, but it can be done.
For example - "Ubuntu Boot To RAM "
There are some Raspbian efforts, but it does still require some manual effort.