The most common and most likely answer to this crossword clue is the 11 letter word BIBLIOMANIA
I've seen this crossword clue in The Times
B
I
B
L
I
O
M
A
N
I
A
More clues leading to the result BIBLIOMANIA
Buddy explains!

The straight part
We know that "passion for shelfstacking?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case passion for shelfstacking? = bibliomania.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BIBLIOMANIA mean?
BIBLIOMANIA noun- A passion for owning valuable books.