So I spoke to the developer and of a Lemmy login, they said
great question. my thought is no but also yes.
The current login via (Mastodon|Bluesky|Threads) is for users who want to add their review to their existing microblogging feed, but Lemmy is not primarily for microblogging.
However, I do think it's valid use case to post a book review to a forum and interact with members of that forum. This does not require login via Lemmy, but instead can be achieved by adding Group feature to NeoDB and make its federation compatible with Lemmy.
When given a further nudge, they responded
thanks, I'll think about it. neither is trivial efforts, will probably take a while.
Also regarding web fiction like featured in [email protected]
Web fiction is an interesting topic by itself, there are currently some debate among NeoDB.social users about if/how that should be managed in the catalog.