Ask HN: What are some promising tech I should look into?

Hi HN, for the last couple of years I've been away from the whole tech startup scene, but now thinking about getting back to building something.

But I'm kind of lost on what tech fields are promising nowadays, and worth working on.

Basically I want to work in a space that has potential to grow significantly in the next couple of years, and trying to do some market research. What would you recommend? (AI? Mobile? The more specific the better)

Any suggestion will be appreciated.