No doubt about points 1. to 5, mediawiki is becoming a kind of standard… It would definitely be interesting to support more than one wiki format. As a matter of fact, one can already write pages in WikiRestructuredText.
With future versions of the WikiEngine, it should be possible to write a different Wiki parser and "plug" that one into Trac, either as the default syntax or as an additional one.
Once such a plugin exist, there could be some discussion taking place if we should ship Trac core with this alternate syntax (or less likely, replace the simpler MoinMoin inspired one by a Mediawiki compatible one), but not before…
That being said, there are a few tickets opened that aim to integrate some of the good things from Mediawiki, see search:?q=mediawiki&ticket=on
See also WikiCreole for efforts on getting the TracWiki syntax more "standard".
Then for points 6. and 7., referencing pages into other wikis (like Wikipedia) can already be done using explicit InterWiki links (e.g. MediaWiki:InterWiki).
Proposing a link to another Wiki on the new wiki page, i.e. when you follow a link to a non-existing page is an interesting idea, but is probably also best done with a plugin.
I'm pretty skeptical about points 10. to 12…
Finally, CamelCase haters (hi Pierre!) are already taken into account, as one can create any kind of WikiPageNames, and it's possible to turn off the generation of new page links when the wiki text contains a CamelCase word for which there's no corresponding wiki page (see TracIni#wiki-section).
