I'd like to see some of the smaller, short haul airliners in 1/72 rather than traditional 1/144.
I'd like to see Revell-Germany update their 1/72 Dornier 228 and the old Matchbox Dornier 28 Skyservant (assuming they have the molds for it) and re release them in civilian variants.
I'd also love to see Esci's 1/72 Fokker 27 make a comeback, its one of the few Esci kits I can trully say I enjoyed building.
Hobbycraft has a 1/72 DeHavilland Canada Dash 8 which is worthy of reissue.
I once saw a 1/72 Boeing 737 at an antique and collectibles show, but I didn't have the money for it. If I recall correctly, it was put out by Nikko.
A 1/72 BAe 146 would be really great in my opinion.
In the way of general aviation, yes the subjects are out there, its just more of a search. I'd like to see AMTech reissue AMT's 1/48 Beech 17 and Stinson Reliant kits with the same attention to detail as they have to the military subjects they've covered so far.