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.