This is digressing, but is such switching really possible, mm_flynn?
There are many cases in airways routings where being able to fly a VFR section within an IFR route would be a useful way to do a shortcut - where there are no airway routes for example. The gotcha is that upon completion of the VFR segment one would have to get a fresh IFR clearance from ATC, also hoping that they have not in the meantime binned the IFR flight plan.
One can understand going VFR - IFR - VFR (on a Z FP) because ATC don't have to do anything special; all they see is the contiguous IFR section which is all that enroute ATC care about.