I've seen guitars done like that before. The extra strings don't get played, they just resonate when you play particular notes on the other strings and make the sound a little fuller.
I wonder what the tuning is on the vintage two stringer is...and if it would be close to bass or treble strings...would be neat if it could be for picking but the neck is too close to the body....
I believe the harp strings can act as bass notes... I wouldn't mind having one to mess around with. I know a man who custom makes guitars who makes harp guitars with similar configurations.