I have managed to do multiple-line fontification in Emacs (and I think in org) using hi-lock mode: M-x hi-lock-face-buffer <REGEX> RET italic RET
But
I can't for the life of me get that regex back which could span
multiple lines. I was sure I grouped '.' and the newline character
somehow, but I can't reclaim it. Maybe someone else has an idea.
If you get it figured out, you can then write the hi-lock regexp's
into your file, and set things up so that they get read every time the
file is loaded (with or without confirmation).
It worked for
me in a limited trial but I'm not sure how hi-lock would interact with
org over the long haul. It certainly has the potential to slow things
down, but I never noticed it.