Well, ahum.
I have actually managed to boot os3.5 on the cd32, although not from the original CD. I made my own bootable cd with os3.5-files.
I assume it would also be possible with os3.9, although the dock and other utils might need more memory, but os3.5 is very much possible.
OS3.5 also has the extended wb-functions which could be fun to play with.
What to remeber when doing these cd's is to include and start the Noreset an Joymouse progs. Also, something to emulate a keyboard with joypad would be great. Began on such a project, but it never got completed.