A new version of Pandoc, V2.11, has been released. The biggest change has been that the previous bibliography filter executable, pandoc-citeproc, has been removed, and a brand-new citeproc system is now directly integrated in the pandoc executable. The new citeproc system is much faster, and much more compliant with the CSL spec (CSL files do the styling for your finished citations and bibliographies). Pandoc can now directly transform BibTeX bibliography database files and even convert them into formatted bibliographies. Lots of other improvements as always (note if you use pandocomatic, hold off on upgrading as a new version supporting V2.11 will take a few more days to be released):
github.com/jgm/pandoc/blob/master/changelog.md
The citeproc system can be compiled to an independent executable, which means it could be utilised by Scrivener during compilation to generate bibliographies. For that to happen, the compiler would need to parse temporary citations, pass them to citeproc and insert the formatted text returned.