Ephemeron? Improving the GC?

[Ola Fosheim Grøstad]

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?