Rick, I certainly would not laugh at that idea but I would wonder about what gauges of stings would need to be used. The higher to strings shouldn't cause a problem with standard mandolin strings but mandolin D to guitar G is by my reckoning 5 semitones higher and the G to the G is 7 semitones higher. I'm a bit brain dead at the moment but I think that the mandolin 3rd string would make the 4th string on that tuning leaving someting else required for the 3rd string.

Of course, if you were to use that tuning, there would be nothing wrong in using pairs of strings either as with a 12 string guitar.

Jon