We should first finally decide whether we even want audiobooks on bookbrainz.
Have you read this thread?
Yes, we have the format choice “audiobook”, (we have also the choice “library binding”, which is nonsense obviously 
- both are remnants of the earliest version of bookbrainz), but we don’t have a single option for sound related credits (reader, narrator, studios etc.).
So we should decide first. Do we want audiobooks in bookbrainz?
And if the decision is yes for the majority of users, the next question is: Why don’t we import all audiobooks from musicbrainz at once?
So we need a decislon…