If you are interested in working on any of these,
email bug-texinfo@prep.ai.mit.edu.

* Use Automake.

* Use a config header file instead of @DEFS@.

* A detexinfo program, like detex or delatex.  This command would
  strip all the texinfo commands out, and would be used as a filter on
  the way to a speller.  An option would be to NOT strip comments out.
  makeinfo --no-headers come close.

* Change bars.  This is difficult or impossible in TeX,
  unfortunately.  To do it right requires device driver support.

* The dark corner symbol for the gawk manual.

* Better i18n support, including support for 8-bit input
  characters.  Requires fonts, and the DC fonts are not (as of this
  writing) free.

* @exercise/@answer command for, e.g., gawk.

* @figure.

* HTML output in makeinfo.

* Include a complete functional summary, a la a reference card, in the manual.

* Use @ as the escape character, and Texinfo syntax generally, in the
  table of contents, aux, and index files.  Eliminate all the crazy
  redefinitions of every Texinfo command (which lists always seem to be
  incomplete).

* Improve the manuals for makeinfo, standalone info, etc.