My first thought is: why would someone want such a configuration?

After pondering this for some time, a light bulb goes off!!! (I'm a little slow). Of course!!!!!!! Think of those who hunt with a single shot for DG and backed up by a good PH with a stopping rifle... The possibility of seeing incidental plains game is very high. Maybe a .470NE combined with a 9.3x74R or some such other combination?

I would not personally hunt elephant or other DG with a single shot (leopard from a blind being the exception), but others quite happily and successfully do - witness the Boddington on Buffalo DVD series.