Please do not include it in MediaWiki at all.
This is my opinion. I defer to the judgment of others. But I think it
is a perfectly awful idea.
Your idea of MediaWiki may be different than mine but I see nothing
wrong with including it in the extensions module and giving Matt CVS
access to maintain it if people want to use it on their own wiki's
(note that I don't have CVS admin access).
However I agree that something like this should not make it into the
main syntax or the main distrubution for that matter.