Here is my 'wish list'....
Lighter unit all around
Better built
Aluminum, one sheet roof (I had one for 15 years and it was as good when I sold it as when I bought it.
Stainless screws all around for seals, moldings and any attachment points.
Compressor fridge (I have one now, a Waeco) beats the absorbtion fridge hands down.
Truma heat and hot water. Eliminate the hot water heater entirely. Eliminates all the heat ducts and mouse houses...
Torflex axles on trailers with grease fittings and disc brakes.
I could go on forever but that is a good start.