My biggest complaint with library management tools, and I think this applies to Librari as well, is the lack of multi-user support. I have a lot of books in my "home library", spread out over a few rooms. But I'm not the only person interacting with this library. Their are books on the shelves that "belong" to other people in the house, and we all joint manage the books. Sharing logins can work, but misses out on so many things that we would like to have.
My dream tool for this would allow multiple people to be "members" of a library, and be able to belong to multiple members themselves. They could collectively manage things like metadata, like what books are on the shelves, but could have individual things like ratings or tracking what they've read.
Plex is actually a really good example of this. I hope some day to find a tracker like that for my books.