I guess there are two issues here (at least)
First off, this IS the FAA RECAT program, Recategorization of wake turbulence separation... not MRS or other separation, but specifically wake turbulence
As you can see, they have detailed the wake and non-wake related operational issues, BUT for the wake turbulence minima...
the minimum, even between same aircraft is still MRS...
Second, as the mechanics of wake generation and transport are not generally understood, especially in the final phase of flight, with the specific danger zone being one wingspan in altitude, it is lemming talk to bring them that close at the threshold.
Wake encounters are reported by the same people who are held responsible for the encounter? Cant imagine why there are few encounter reports...