>
> 3. Handling of citation links in the various export engines
> Functions must be written to handle citations in, at minimum, latex, html,
> and org
>
> 4. Interface with backends
> Org should be able to talk to bibtex and zotero databases, at least (and
> maybe more).

The code I wrote should have enough hooks to enable this.  But I haven’t
looked at zotero at all.  If zotero support is important to you, you
could investigate the “lookup types” in the citation code I wrote, see
if they are adequate, and try to use them to implement zotero lookup.
From the docstring:

"Types of citation lookup backends.

Alist from type to list of:

- Function called at the beginning of export, with the rest of
  the keyword line after #+BIBDB: type, and the info plist.
  Should cache whatever it needs in the info plist.

- Function to lookup a citation.  Called with the key and the
  info plist.  Will be memoized by
  `org-export-cite--lookup' (TODO).  Should return an alist of
  keys and values about the citation (author, year, title, etc.)

- A boolean; non-nil = this lookup type is remote.  All local
  lookups will be tried before any remote one is.
  TODO: not yet implemented"