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.
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.
For parsing MediaWiki in Python, check out mwlib [1], which was part of cooperation between Wikimedia Foundation and PediaPress. It's neither very complete nor very fast, but you might be able to hack up some LaTeX conversion with it.
I actually wrote a subset-of-MediaWiki parser in C#, which stayed at the "subset" stage because of the ridiculous complexity and corner-cases that crop up even very early.
Another example of the imperfect but working implementation winning.