I'm not qualified, but "The technology could serve as a renewable fuel source in high altitude and polar environments" from the first paragraph of the article suggests to me that the potential is pretty limited.

I suspect it'd be most practical in areas with limited heat and were other alternatives aren't as handy.

There's also a few areas where combustion engines are more practical than electric ones and hydrogen engines could be used as a stop-gap solution until electric alternatives catch up; there's only so much humanity can do at once and using combustion engines with renewable fuels could reduce emissions while we take our time focusing on other areas.