In the experimental multilingual Zotero fork, I've added an export
option for "Citeproc JSON", that exports the data as it would be
shipped to the CSL processor. It has indeed proved very handy for
debugging, and for quickly building test fixtures against reported
faults. It's a special-purpose thing, and probably not suitable for
inclusion in Zotero proper, but it's handy for those who have a use
for such a thing. I won't go there myself, but an ambitious soul could
refactor the code to work as a supplementary plugin, to make it
available in official Zotero.