[novok]

Often though, many successful VC startups start from a niche and expand from there. For ex: uber started with luxury black car service only in SF (a niche) and then expanded into normal cars, carpools, food and the rest of the world. I think the real requirement is a foreseeable future that you could potentially expand into a bigger $billion market.

Small niches that have proved themselves are often more attractive from an investment standpoint.