* mut Option<T> -> Option<*mut T>?

This is admittedly changing the question :slight_smile: ; at this point I'm convinced this is the wrong problem to solve, and instead I should be re-designing to get rid of the Option<My_RcBox<T>> into something that does not use the Option. I.e. see Help redesigning attempt at rc_arena for full details on what led to this particular problem.