A longer scale would be harder to play on the lower frets ... Michael Angelo has a 29 frets guitar and it seems to be 25.5" scale (not sure) , and he manages to reach the 29th.

What's actualy bothering my mind is the 7th frettless string thing , you mean you're going to cut the frets right after the 6th , yeah ? Now , you'll also have to leave a plenty of space for the 7th string not to hit the frets or go out of the neck by mistake ... That would be one heck of a guitar fretboard !

I suggest you add a Floyd Rose tremolo too , cuz it seems that you want this axe to have almost everything ,like a swiss knife ;) .