Speaking of reasonable: I always thought the use of single character markup (e.g. * for bold), visual markup (bold instead of emphasized), several modes of emphasis (italic and bold instead of just emphasized, but maybe I just used latex for too long), and excessive "simple" markup instead of some sort of language were a mistake. I personally would rather call a simplified latex + "simple" markup for the most frequently used constructs "reasonable". I also liked the approach deplate took (http://deplate.sourceforge.net/deplate.html), I would have preferred a more latex like look though.

As a long term markdown user I also don't think "reasonable" is a relevant criterion. Markdown definitely is not reasonable but it's useful.