The reason == is escaped as \== is that only in this case this is
problematic, if all markup characters were escaped we would beed to
escape also a single occurrnce of = to \=. No?
I don't see any problem parsing \=\= or any multi-character markup (eg \@\@) to plain text - I don't think it matters if \= and \=\= is ambiguous as all you're only interested in producing the '=' character, free from interpretation as any markup.
How about I fix the failing tests and in the process make sure it all works as intended and if so check in the changes. We can always roll-back if I've missed something.
Nick