Your code modifications for
http://wikitolearn.org/ are interesting. I'm
pretty sure that KDE policies don't force you to fork MediaWiki
extensions locally, so your patches are definitely welcome upstream.
I'm not sure what you mean with your point about <dmath> being rejected
by the community; perhaps you refer to some performance decision made by
WMF. If your modifications to Math are incompatible with some decision
of the maintainers, you can ask a different repository on gerrit or
another branch on the same repository, so that non-WMF users can use
your code.
As for your comments on chapters and drafts, I don't see anything
incompatible with how Wikibooks and Wikiversity work. If you have a
solution for what we call "book management" i.e.
https://phabricator.wikimedia.org/T17071 (worked on by Raylton and
others with
https://meta.wikimedia.org/wiki/Category:GSoC_Mediawiki_Book_Experience
), that's especially interesting.
To reach the Wikibooks and Wikiversity community, the best way is to use
a medium that can involve their active editors, such as their mailing
lists (cc'ed here) or wikis.
Nemo