IIRC, JFS itself supports all characters except the colon. OS/2, or perhaps just cmd.exe, also disallows \ as it is the directory separator, as well as / and silently ignores ".
lots of utf8 chars that would be hard to manipulate on the cmd line.
I learned on an Apple II+ clone, you could enter any ASCII character except DEL (used as the cursor) with the keyboard and could use CTRL characters in a file name. Could have a file name like foo^H^H^Hbar which would look like bar in a directory listing and very hard to manipulate from the command line if you didn't know about the CTRL-H's.