Besides WikiCreole, someone else is implementing pluggable parsers of wiki syntax without an intermediate language, or say, the intermediate language is flex. This guy, Ping Yeh, will introduce his pilot work on Wikimania: http://wikimania2007.wikimedia.org/wiki/Proceedings:PY1
Actually I'm imaging that if this flexible parser idea, as the input part, connected to some kind of wikiwyg formatter, as the output part, they may solve similar problem of WikiCreole and pull the day of "WYSIWYG <-> XHTML" closer to us; by this kind of interpretation of Brion's comment, I second it.
Sincerely, /Mike/