I had not read about this concept, but stumbled over it yesterday when reading up on the C++ garbage collector Oilpan:

https://en.wikipedia.org/wiki/Ephemeron

If D is going to continue with a strong focus on having garbage collection, then maybe it is time to discuss how it can be made more useful?

Ephemeron seems to be a very useful concept for people writing frameworks.

Or is it already available in D?