I'm not thinking very hard about it, but that second bullet sounds like a really good idea.
http://telemetry.mozilla.org/#filter=nightly%2F39%2FCERT_VAL...
Ignore the graph and match up the table below with this C array:
https://dxr.mozilla.org/mozilla-central/source/security/mana...
If I'm understanding the meaning of "Bin Number" right, not all of the 0s are surprising. But some are. For instance, the AOL CA hasn't been used to sign any certs that have been seen. (I guess, in a sense, that's not really surprising...)
I'd be cool if someone better at front-end than I could present the data with useful labels, and also mark each CA by whether it's in the non-Mozilla roots.