Do you use Singleton's _instantiate? method?

I’m in the middle of re-implementing portions of JRuby’s stdlib to fix
threading problems and to take better advantage of native threads. In
the process, I ran across Singleton’s _instantiate? hook. I don’t think
I’m going to be able to make it work in a backwards-compatible way, but
then I’ve never heard of anyone using it either.

Before I get rid of it permanently, does anyone out there use it, and if
so, what sort of things do you use it for?

Thanks,

-mental