VR, AR, AI. Three two letter buzzwords. All of them have massive unexplored potential on the desktop.

> It's actually shocking how difficult I'm finding it to answer this question.

You are asking the wrong question, because you are looking at the existing market. You need to analyze trends, news and cutting edge science, have imagination, vision and forward thinking. That's obviously also hard, but it's not like looking for an empty field in the forest where you want to plant your trees.

You might find "Blue ocean strategy" a good book.