I guess it depends on what you mean by a "niche". Because I'm familiar with things like healthcare, financial services and business in general i tend to stick with what I know best. This is what Warren Buffett, some say the greatest investor in the world does.
You might say these are my "niches" left of the dot, and since most of the really good .com's right of the dot are already taken, i focus on new gTLD's. Most recently I've been focusing on .online and .link, extensions that actually communicate something unlike .com, or .xyz.