Selectively suppress generation of typeset output

Taking inspiration from syntonly.sty:

\documentclass{article}
\makeatletter
\font\dummyft@=dummy \relax
\def\suppress{%
  \begingroup\par
  \parskip\z@
  \offinterlineskip
  \baselineskip=\z@skip
  \lineskip=\z@skip
  \lineskiplimit=\maxdimen
  \dummyft@
  \count@\sixt@@n
  \loop\ifnum\count@ >\z@
    \advance\count@\m@ne
    \textfont\count@\dummyft@
    \scriptfont\count@\dummyft@
    \scriptscriptfont\count@\dummyft@
  \repeat
  \let\selectfont\relax
  \let\mathversion\@gobble
  \let\getanddefine@fonts\@gobbletwo
  \tracinglostchars\z@
  \frenchspacing
  \hbadness\@M}
\def\endsuppress{\par\endgroup}
\makeatother

\begin{document}
Some text.
\suppress
This text \emph{will} not be seen in the generated document.
\endsuppress
But this text will.
\suppress
And this text won't again.
\endsuppress
This will show.
\end{document}

However rules, radical bars, fraction bars and some other things (mostly math) can escape.

One idea that occured to me was to use \nullfont:

\documentclass{article}
\long\def\suppress#1\endsuppress{%
  \begingroup%
    \tracinglostchars=0%
    \let\selectfont=\nullfont
    \nullfont #1\endgroup}
\pagestyle{empty}
\begin{document}
  \suppress
  This text will not be seen in the generated document.
  \endsuppress
  But this text will.
  \suppress
  And this text won't again.
  \endsuppress
\end{document}

Super-Caveats

1. Maths are not hidden
2. I don’t know LaTeX well enough to tell if I’m doing something really silly in the above.