Several sites have MathJax enabled, so there is obviously some room for site-specific markdown.
Therefore please can we have markdown tables here on dba.se? There is an open feature-request for this on mSO, but whereas it is hardly a key feature for a programming Q&A site, a significant percentage of our questions and answers contain tabular sample data, and real tables will make them neater and easier to read.
All we can do now is use ascii art but this has a number of drawbacks.
If the feature request goes through I'm pretty sure Jake Feasel will be happy to tweak SQL Fiddle to make it produce compatible markdown.
I've discovered that MathJax isn't implemented as a markdown extension after all, it is a script that runs on the page. Apparently the 'Go' board game site had it's own code as well for displaying board positions, but I'm not sure whether that was markdown or a script.