I have done some research. The POSIX 1.b extensions aren't used on any supported system (neither Linux nor BSD, Solaris or AIX).


random832@fastmail.us has compiled a list of even more file types:

Heirloom toolchest "ls" supports:
http://heirloom.cvs.sourceforge.net/viewvc/heirloom/heirloom/ls/ls.c?revision=1.9&view=markup
http://heirloom.cvs.sourceforge.net/viewvc/heirloom/heirloom/ls/ls.1?revision=1.5&view=markup
S_IFNWK HP-UX network special file
S_IFNAM  XENIX special named file
S_INSEM XENIX semaphore subtype of IFNAM (looked up from s->rdev)
S_INSHD XENIX shared data subtype of IFNAM " " " "

Of these, GNU coreutils ls only supports doors and whiteouts.

Chasing after a random hunch (something about AIX), I found these:

http://cd.textfiles.com/transameritech2/EXTRAS/JOVE-4.6/ASK.C
S_ISHIDDEN Hidden Directory [aix]
S_ISCDF Context Dependent Files [hpux] 
S_ISNWK Network Special [hpux]

http://lists.gnu.org/archive/html/bug-gnulib/2012-12/msg00084.html
S_ISMPX AIX "MPX" file (multiplex device?)

https://github.com/gagern/gnulib/blob/master/tests/test-sys_stat.c
has a massive pile of macros with no comments
S_ISCTG S_ISMPB S_ISMPX S_ISNAM S_ISNWK S_ISOFD S_ISOFL S_ISPORT

http://lists.gnu.org/archive/html/bug-gnulib/2004-08/msg00017.html
S_ISOFD Cray DMF (data migration facility): off line, with data
S_ISOFL Cray DMF (data migration facility): off line, with no data
S_ISCTG Contiguous
(It's possible that these may not be file types)

http://doiso.googlecode.com/svn/trunk/Source/mkisofs-1.12b5/include/statdefs.h
S_ISMPC  UNUSED multiplexed c
S_ISNAM  Named file (XENIX)
S_ISMPB  UNUSED multiplexed b
S_ISCNT  Contiguous file
S_ISSHAD Solaris shadow inode

http://www.opensource.apple.com/source/gnutar/gnutar-450/gnutar/lib/sys_stat_.h
S_ISMPB /* V7 */
S_ISPORT /* Solaris 10 and up */
S_TYPEISSEM S_TYPEISSHM - macros to check the XENIX IFNAM types
mentioned above
S_TYPEISMQ S_TYPEISTMO