...in O(n log n) time per handle fetch (if I'm reading the code right).

The module seems to implement a Least Frequently Used cache (though it calls it Least Recently Used cache), and does so by incrementing and re-sorting on each request for a handle. And then there's this: "The module functionality relies on symbolic references, so things will break under 'use strict' unless 'no strict "refs"' is also specified." So the only way to use the module is to wrap the code that uses it in a scope block and specify no strict 'refs'; for that block. Talk about the implementation leaking outward into the interface!

It's hard to believe it's still in the core.

I think that a Fibonacci Heap solution would work nicely. Inserts (adding a handle) are constant time, remove least (dropping a seldom-used handle) is O(log n) time, change priority (calling for a handle and incrementing its use count) is a delete+insert (O(log n)). Of course the devil is in the details. If I find some free time I might give it a go and see how it works out.