I think the key feature of great AR is that we don't have it yet, so there are no limits on what capabilities you can imagine it could have.

If you instead think of each dreamed about great AR application as a smartphone app, an uncomfortable realism creeps in about how apps work and that someone has to build and integrate them

"But if I could put on glasses and see what’s going on with my car and then be guided through that process, that would be cool. "

It would. And if we built that smartphone app, it would be really useful today. But doing that, for the general case of "what am I looking at, and how do I fix it" is AGI-hard