The most interesting thing about those less energy/ pressure replacements for the Haber process have is the promise of being able to produce nitrogen fertilizer from renewables near the fields they’ll be used on (and so reduce CO2 emissions from Haber - and from transport). There’s a lot of ag land currently in use in places like Africa and South America that are dependent on this kind of amendment to be productive.

I'd expect that burning the ammonia in an IC engine (and so producing NOX, which if anything is worse than CO2 for global warming) is very far down on the list.