This is my proposal:
+1 for your proposal.
I feel sphinx.ext.coverage is one of candidate. I've never used it, so I can't say it should be bundled or not. But I would not be able to maintain it...
Note: htmlhelp (chm) was now deprecated. So it's time to split package from core.
I just made a repository for jsmath!
https://github.com/sphinx-doc/sphinxcontrib-jsmath
Finally, I separated packages which I proposed!
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This is my proposal: