Bruce and I looked into this UI approach in
https://github.com/jkitchin/org-ref-cite/issues/9. Bruce and I discussed and worked on this for almost two weeks. There are 70 comments in this issue.
There are opportunities now to annotate completion targets, which you can see in the link above. The annotations are not selectable though during completion, and this implementation was not too fast as I recall. You probably should also augment the tooltips like this because you have to be able to tell what a citation format is in the future too, not just at insert time, e.g. suppose you are reading work of a collaborator. It was hard to write, and ambiguous in ways, e.g. what is the export backend you want? The annotations should differ for LaTeX (where you want to see the latex command) vs HTML (where you probably want to see the formatted CSL cite)...
We did not surmount these challenges at the time. Maybe others will succeed in this another day.
John
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Professor John Kitchin (he/him/his)
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803