My own kcite is rather easier to use than AcademicPress. You put an
identifier in a shortcode, and it gathers all the metadata. Only the
identifier stays in the database, so error fixes to the source database
percolate (with a long caching period!).
It doesn't support CiTO yet; I would add this (it is trivial to do), if
I could be convinced that anyone is actually going to use it. At the
moment, I can't see what advantage the author is supposed to get from
doing so.
Custom fields won't work with this approach, because the metadata comes
from elsewhere. What do you want to do with the fields? To me, it would
make more sense to have an independent markup -- then you could surround
cite tags with additional metadata tags.
Finally, OAI export -- kcite doesn't do this, but it will allow you to
recover all the cites in a article as JSON. A bibtex export would be
quite nice, come to think of it. I should add that.
Phil