Adding more humanitarian/domestic cargo types to the cargo system would be very interesting.
iT iS a CoMbAt SiM aside, cargo helicopters and aircraft are used extensively for these missions and would open up many different experiences in DCS. How many cool videos are there of transport aircraft doing firefighting?
With that in mind, here are some potential humanitarian cargos that could be implemented.
Bottled water
Larger water containers
MRE's
Grain Bags
Cardboard Boxes
Jerry Cans
Medical Supplies
Shelters
Plenty of pictures are available to create a unique pallet design for each. You could even have multiple skins from different organizations (USAID, Red Cross, UNICEF, etc.)
From the supply system standpoint, it might make sense to have this as a separate tab since our current ones are very focused on A/C, weapons, and fuels. However, I think having a fuel bladder that can transfer fuel without being unloaded would also be interesting.
It would also be nice to have some payload loaders/handlers to accompany these and the other cargo types, but I'll take bets on whether we get those this decade.