If there is enough space to have a room full of books, it would be better used as a publicly accessible set of stacks. The only real reason to have a librarian-only room is for books that are rare and valuable.
Someone needs to take up Carnegie's mantle and finish the job which he began.
What's the limiting principle you propose? It has to be something real libraries and library funding sources can take action on, because they have to take real-world actions on them. So this is not a time for aspirational speeches or vague exhortations to "do more", which is the exact opposite of a limiting principle anyhow. What is "enough"?
As I noted, it's a pain for me to have to drive down to DC to get access to a book which _used_ to be in the local library system, but isn't anymore, or to purchase my own copy (which wasn't previously necessary).
My current library is around 2000 square feet and I acquire around 1000 books a year, so I have to toss around 1000 books a year, because they're made of matter and take up space.
https://www.abebooks.com/servlet/SearchResults?ref_=search_f...
In the first edition, he was depicted as a large creature, and Tolkien was upset about it, and in the second edition, changed the description to small.
This information was gathered by a rare book seller who's videos I find immensely interesting.