Perl in general:
Add ftw or find?
Add a parsing mechanism (user specifies parse tree, perl parses).
Arbitrary precision arithmetic.
File calculus (e.g. file1 = file2 + file3, file1 =^ s/foo/bar/g etc.)

MS-DOS version of Perl:
Add interface to treat dBase files as associative arrays.
Add int86x function.
Handle the C preprocessor.
Provide real pipes by switching the processes. (difficult)
Provide a list of ioctl codes.
Check the ioctl errno handling.
I can't find an easy way in Perl to pass a number as the first argument
  to ioctl.  This is needed for some functions of ioctl.  Either hack
  ioctl, or change perl to ioctl interface.  Another solution would be
  a perl pseudo array containing the filehandles indexed by fd.