Good and important topic mate!
I think this is a problem with every channel/business/media format - the moment you are reducing the focus of a channel to a niche, you are limited of topics. Obviously. But on the other hand a niche channel can grow much faster because people know what they can expect and you will receive active followers and nerds :P
I think to extend the video formats to Q&A, reactions and so on can help a niche channel to find more topics while keeping the main focus on that topic.
I subscribed to a very good example "Ikopta" (on youtube) about drone flying. "not another drone channel" you would say.. But he makes a show called #mail - where he answers questions of the community while reacting to their videos. Thats unique and worth to follow.
Thanks for sharing your dream with us :)
Yes niche channels grow a lot faster. I think many YouTube channels do that - start as a niche channel and then when they grow large enough, the change to generic channels to find more topics.
Q&A is a good one.