Interesting. The next question, of course, is "Can you scale it up to replace 160 exajoules of energy currently provided by 30 billion barrels a year of oil ( https://en.wikipedia.org/wiki/... ), or will it remain forever a niche player?"
Current world-wide ammonia production is mostly going to agriculture and is only about 130 million tonnes. 130Mt * 1000kg/t * 4318 Wh/kg * 3600J/Wh ~ 2 x10^15 Joules.
However, the goal is not to replace oil, but to replace gasoline for cars. Natural gas production, has plenty of scale (4.3Tm^3)*** and ammonia production generally scales easily with natural gas production. Also, only about 1/2 of oil production you quote is for gasoline for cars and trucks.
The question is if it is worth diverting natural gas to cars or not (vs converting it into electricity or using it for heating/cooking). Even if it was desirable, it's not an easy question on exactly how to do this because for cars, alternatives to ammonia production are to compress or liquefy natural gas (CNG/LNG). The benefit of ammonia is really is in industrial CO2 containment, but CNG/LNG would be easier to do at a large scale...
However, if there were an economical way to create ammonia from atmospheric Nitrogen w/o using Natural gas, there might be something to all of this... People are working on it, but nobody has got anything commercially viable yet...
***To convert natural gas to barrels of oil equivalent: 4.3Tm^3 * 1BOE / 170m^3 = 25MBOE