Lars Hellström writes:

 > Would it break anything if the LaTeX core would say
 >
 >   \ifx \protected\@undefined \def\protected{} \fi
 >
 > and \protected was used before each definition of a LICR command?

probably not (well, probably yes :-) i have yet to see a single change that
doesn't break something, but for most purposes that should be a clear no).

However, that would be fairly in efficient way to use the eTeX feature, ie if
eTeX would be unconditionally used one could run far more efficient code since
a lot of that \ifx\protect\typeset@protect could go away (and an LICR command
on top-level expansion could be reduced to just two tokens)

however, as a compatible start that actually works with TeX one could simply
go

 \ifx \protected\@undefined \def\protected{}
 \else
   \WARNING-This-may-loose-characters-if-you-are-not-careful-better-use-etex
 \fi
 \protected\def\@current@cmd@math....

and that should do the trick

frank