LPG freezing at height :
Think about it. I had a LPG forklift until last year (now electric, a lot less hassle). This was in use @ Portsmouth, lets say 50 ft above see level. We always had problems with freezing of the gas. To prevent it the gas come from the bottle and staight into a pressure valve that has a water jacked aroung it from the cooling system. Theory being the running engime would stop the gas freezing. But with short use runs and winter months, it was a pig. (1991 mitsubishi compact 25 if anyone wants to know).
Now most aircraft have no water cooling to aid anti freezing and would you really want a fuel that 'could' freeze very easily and cause things to go very quite up front.
Petrol and JetA1 are perfectly good at what they do