I think that would be the best syntax since pandoc already uses it. Displaying math should be left to other things like mathjax though.
I think there is no syntax for superscripts and subscripts because Gruber’s original markdown syntax did not contain it and I believe one of the goals of this project is to address the flaws, bugs and ambiguities of the original Markdown.pl implementation.
Therefore, I think it’s best to have this in the ‘extensions’ category.