As the six string banjo made it possible for guitar players to play the banjo with no learning curve, so did the tenor and plectrum guitars make it possible for banjo players to play the guitar with no learning curve.
This summer I had a chance to play a mandolin body with a five string neck and it sounded great played clawhammer style. I've also had a chance to play a five string Dobro and liked the sound it made (not at all like a slide Dobro).
Tommy Tedesco, one of the most recorded guitarists, played banjo, mandolin, bouzouki, and many other fretted instruments. He tuned them all like a guitar, and used his considerable guitar skills to play them.