Typically, PoLR is seen as the the thing that's "hard" to do. I think that's a bit of a simplification of what PoLR is, but that's how it's generally understood.
I would like to suggest something harder: Using your role function as a creative function. I think that's really much harder than PoLR. PoLR isn't really a big barrier to "accepting subtypes." And role isn't really that hard if you're using it like your look-alike or super ego type. But using your role function the way your conflict and supervisee use it: That's what people hate to do.