Hash-tables containing references to hash-tables

[Nordlöw]

Is it possible for a hash-table to contain a *reference* to another
hash-table, similar to how we can build arbitrary graphs using conses/
lists and setf?
If so how? If not, is there reason for being so or is it just an emacs
todo?

If we have
  (puthash parent-key (make-hash-table : size CHILD-SIZE) parent-hash)
then I want
  (gethash parent-key parent-hash)
to return a *reference* to hash-table contained in parent-hash.

I already have a working code for this but I am uncertain how this
will perform when CHILD-SIZE is really large.

/Nordlöw