A great niche to get into would be Internet censorship avoidance in countries where Internet freedom isn't a thing. As an expat living in China, I can tell you that there are only a few companies that do this successfully (among them Astrill and ExpressVPN).

Operating this kind of VPN comes with its own set of unique technical challenges, such as avoiding DNS poisoning and offering the best protocols to use. Spinning up a homebrew solution on DO just doesn't cut it as an end user, so we rely on companies like these to provide targeted solutions.

A VPN provider that can focus on avoiding common blocking techniques would be very valuable to a lot of people.