Anything besides gasoline is going to take changing the infrastructure big time!
If it is Ethanol - then changing the raw material source (hideous agricultural implications!),
changing the manufacturing methodology and equipment - the delivery infrastucture
can remain essentially unchanged.
The US Gubment will have fits with their anal desire to tax a consumable fuel!
Imagine ethanol available to drink for pennies.....(?)
Talk about getting pickled!
If it is Hydrogen - the entire infrastructure will have to be changed with gross
implications for manufacturing (w/o burning carbon based coal or oil),
delivery (dangerous high pressure tanks or safe metal hydride containers), and
complete engine specifications changes.
If Electric - total change over to non-hydrocarbon, non-combustion "motors"
and continually upgrading battery technology and slow chargeup times.
Unless they can develop "large capacitor" based electric storage systems.
Electric systems presents its own dangers - electrocution, massive shorting
of batteries (explosions), corrosion ad nausium...etc.
The next few generations will face massive changes just as our Grandparents
lived thru "horse and buggy" to automobiles and flying in the air.
What a change the old folks saw!
Six guns and Indians all the way to Spaceflight even!
You have no idea how fascinating the next 50 years will be!
DoctorBill