The avocado grows on atree that takes about seven years to mature and start providing fruit. It has to grow in areas which are at least semi-tropical.
Now while it might be heart-warming for econuts to belive that avocado nuts can be part of a fossile fuel free future, you’d have to face the fact that most of Mexico, Central and S. America would have to be covered in avocado trees to make a real dent in fuel supplies.
On the bright side, guacamole would be cheap and you could eat it til you were sick.
You say that like it's just a minor detail. The idea deserves serious consideration based on this alone.