Instead of these ballooning regexps, how about just using Chael Hall's standardized "end of body" marker? Even if some people had to add it manually to each message, well, that's not a big deal. But I suspect that the people who have sigs being added by BBS software are going to have trouble adding strange header lines, even if they have the regexp expertise to construct them.
Didn't we go through this at least twice already. Yes, your suggestion is perfectly OK for a "pure" cypherpunks remailer with sophisticated users. It is *NOT* OK for something like the typical anon.penet.fi user from alt.sexual.abuse.recovery or alt.transgendered. And at least anon.penet.fi allows for using the special header lines as part of the message body, to compensate for braindamaged mail systems. But some users might not even be *aware* that their systems add sigs - yes, I've come across a lot of those.... Julf