"Personally I'd be happy to see any markup language becoming the default."
I don't agree with this. All lightweight humane markup languages are not born equal, some are better others, and Mediawiki's is not in the list of the best ones. Now there seem to be a trend towards Markdown, but it should be improved and then, migrating Wikipedia to this Markdown2 could be a real good thing.
Personally I'd be happy to see any markup language becoming the default, regardless which one it is. Having a proper grammar would be a bonus.