I also am happy to see renewed interest in the external frame. My "beast hauler" is an old Kelty.

I would like to see an external frame that is designed for lighter loads. Pack weight should be less than 10% of base weight.

Modular would be a good feature. I have a friend that likes lots of pockets, however I prefer to use stuff sacks for organization. Maybe a single frame with mix & match bags and waist belts.

Needs an exterior mesh pocket for wet flys.

Needs the ability to carry a gallon of water outside the pack.

Quick adjustment of the center of gravity would be nice. I like it low when hiking steep trails but like to raise it when striding out on level ground.
"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra