If DES is a MUST then US software companies will have a difficult time
exporting S/MIME-compliant products.
That's for US companies to discuss with Uncle Sam. It's not something
that IETF should concern itself with.
IETF should concern itself with the quality of the algorithm --
whether it's believed to be of sufficient strength -- and whether it
is available under fair and nondiscriminatory terms.
US export regs are irrelevant unless they somehow prevent a candidate
algorithm from being made widely available under such terms.
Keith