What functionality is desired: -

The ability to have mediawiki markup syntax highlighted appropriately within a <syntaxhighlight>pusedo tag.

Why is this being requested: -

Currently examples of mediawiki markup are marked as
*PRE

• CODE, KBD , SAMP or TT tags in HTML, which are not ideal.
• Escaped markup which is confusing to edit..
• As <syntaxhighlight> blocks but using the "html", "xhtml" lexers...

Having an appropriate lexer for the SyntaxHighight extension will enable those approaches to be replaced with a simple <syntaxhighlight> tag (which can also be cleanly inlined) and the requisite wikimarkup can be entered almost directly with less need for convoluted escapes.

Being able to cleanly quote and include markup examples would help immensely in being able to present certain examples of it.