-- and I think you'd have toneholes on the neck.
Why not? You already get register keys on the neck, why not tone holes? On the soprillo, you have a register vent on the mouthpiece.
Actually, more toneholes is probably not the answer: just need another (altissimo) register vent in the right place. Isn't there a Selmer Paris tenor that has an altissimo vent?
Grant