Regarding overhead bin space.....make the bins an inch or two deeper, so that more bags can go in perpendicular to the bin. And before they get bought and installed, actually test them on real-life carryons. Get some Tumi's and Travelpro's and the like and actually see if they fit. Or better yet, take some of the proposed bins to the WC's in MSP, DTW and some other stations and have members try out their bags in the new bins - and get real-life data!
Adjustable reading lamps and effective air vents also go on my list. Adjustable headrests in both F and Y. Leather seating, at least in F if not the whole plane (I gather they have lower lifespan costs, IIRC).
Just how wide is this aircraft? Is it 767 width, 330 or 777?? Kill the middle seats whenever possible.
Probably a few more things, but that's it for now.