I look for plain text markup what allow extension of syntax through standard way and ability to include/program own writers (or register routines to writer extension points) in order to get final document in different form with handling additional syntax myself.
As I know markdown is limited to making text strong/emphasis...
RST look promising but I afraid that with my limited experience I miss some rich and useful markup language... I just look to http://en.wikipedia.org/wiki/Comparison_of_document_markup_languages and get lost.
PS. For dev docs and personal blog generation.
PPS. Explain why XML, JSON or any of a number of generalized markup languages doesn't meet your requirements
Using Json or XML are not pleased because I want readability of original source format. While I work with DocBook - it is not a funny format for personal blog articles... It must be fun to write... So I look sfor some wiki syntax with extension points and engine which can provide AST.