@ncoghlan
Thanks for request and the pointer to
  http://psf.upfronthosting.co.za/roundup/meta/issue626

I'm also still interested in this topic.
We should add a possibility to configure markup display.

First technical design question: how do we indicate markup?
My ideas:
 # Let us come up with something that Markdown or MoinMo.in do for
 inline markup see https://moinmo.in/ParserMarket/burndown for a
moinmo.in example

{{{
!#creole

}}}

 # go by Content-Type (for files), maybe additional detection my file
suffix.
 Research point: What are the best content types for 
  markup files like creole, markdown or reStructuredtext