As VFR requires navigation with visual reference to the ground,
Is that really the case, legally speaking? I know "VFR on top" is a contentious topic, and not legal in the UK unless you have an IMC or IR, but it definitely does exist in some countries. Also, not every type of airspace requires the VFR pilot to stay in sight of the surface. And the PPL syllabus does require some radio navigation so technically speaking a plain PPL pilot should be able to navigate that way. (Whether the PPL pilot is comfortable with tracking an NDB or VOR is a different matter.)
Obviously if you planned your VFR flight to be flown using ground references/VRPs, then you have to be able to see these, or change the plan. But if your flight was planned to make use of radio navigation of some sort (NDB, VOR, GPS), and planned above the MSA, you would not need to be in sight of the surface, would you?
I'm not questioning the practicality of this, just the legal aspect. Of course, practically speaking you've got to have a plan to deal with engine failures or the eventual arrival at your destination. But I can well imagine (and in fact, will admit to) flying over a layer of ground mist, temporarily obscuring all ground features, when you know that that mist layer will end in a few miles.