Congratulations! You tired of your general practice, did some research, and decided to refocus on a niche practice limited to estate planning for Hittites.
Compared to a general practice, a niche practice will be more efficient, and therefore profitable. And it should be easier to demonstrate expertise in one area of law than in all of them.
Perhaps you intend to create a niche practice defined not by a type of practice, but rather by the nature of the work to be done or service to be provided. For instance, a practice limited to handling summary judgment motions, or administrative writs, or taking depositions and examining witnesses.