Thanks to you and @Joseph_Heck for your quick replies and work!
Thanks for the direct link/hint. Sorry for asking before checking out unidoc (particularly your recently released preview and local commands) and for my delay in responding.
After some futzing, I'm up working now with unidoc's compile command to dump the bson to investigate possible analyses. (Unidoc balks on most of my target packages, and I'm still sorting through how much I can do without standing up mongodb. (Feedback elsewhere)) Consuming the data seems manageable, and the code is pleasantly readable.
For the analyses, please let me know if there's anything I can do to help or motivate the extra work of publishing the binaries. A single snapshot-set for some proof-of-concept prototyping would validate possibilities without tangling too much in versioning (and the snapshot needn't be all-one-version). It would help even to stage partial sets by importance/traffic (e.g., apple+swift/swiftlang, pointfreeco+alamofire+rxswift, swiftyjson...).