I think a better solution would be for foo_musicbrainz to use libdiscid rather than to remove its feature altogether. We want it to be easier for people to add data (incl. Disc IDs) to MusicBrainz, not harder—but we also want them to submit correct data. So either any bugs in foo_musicbrainz should be fixed (it’s good to have multiple implementations of a standard!) or they should switch to use libdiscid for Disc ID calculation (it’s the official and canonical implementation and it’s good to support the upstream of that!).
Either way, as long as the lineage is observed via edit notes or some such, I’m fine with any outcome, as we can go back and determine “bad clients” later. Only issue with that is that it’s most often not given in edit notes what was used to calculate the Disc ID. 