If I was filthy rich, and could experiment on making a new guitar, I would like to see if any of these ideas would work on a Manouche style axe:
1) A tone port (hole) on the upper bout. I don't know how many times I wish I had this inacoustic jams where it is a bit too loud. Sure, people should be able to play quieter, but I don't know if any amount of money would buy you that in some jams I have been in.
2) A height-adjustable bridge like on my archtop, you know thumb screws for the height adjustment. Maybe this would be too heavy and muck with the tone, but it would be cool to try it. If it worked seems like it could give a lot more flexibility. Who hasn't had to resort to shims at some point?
3) A way to use heavier strings, at least 12s or 13s on the top E. I like a very thick tone.
4) A built in magnetic (preferably single coil) pickup that mounts at the end of the neck, and does not cover the tone hole. Tone/volume mounted somewhere easy to get to and still out of the way.
I realize that there are very good reasons these guitars are built along accepted principles, but after all, if Macaferri didn't try something new..........well, you know the rest