A possible killer app might be something for business meetings. Videocalls are already a huge thing, but many feel like they're missing some real personal intimacy in there. If instead of a videocall, you could all be using AR to see each other walk around in front of you, that might make it a whole lot more appealing. If it's done right, you could have the same private one on one side conversations that are common in real life, but just in some AR space.

AR has a clear advantage over VR here as you wouldn't be blind to your real surroundings so you'd still be able to talk with the people in real life too (and not look like a doofus who walks into walls)