This issue sounds very interesting to me for a somewhat different reason.
My problem is that I'm trying to run multiple processes on separate CPUs/cores with os.fork(). In short, the data set is the same (~2GB) and the separate processes do whatever they need, although each fork treats the data set as read-only.
Right after the fork, data is shared and fits in RAM nicely, but after a few minutes each child process runs over a bunch of the data set (thereby modifying the ref counters) and the data is copied for each process. RAM usage jumps from 15GB to 30GB and the advantage of a fork is gone.

It would be great if there was an option to separate out the ref counters for specific data structures, since it's obviously a bad idea to turn it on by default for everything and everyone.