Yea, I was trying to think about the examples of niche first then expand. And niche permanently. Amazon was niche to books at the start but ended up consolidating a fragmented book market before going after everything. You might say Facebook was niche to colleges before inviting the total population. Discount Shave Club was niche to men before well selling out to Unilever. Some companies cater only to beards and can do very well until beards become less fashionable.
Whatever you do, solve a chronic niche problem very, very well and expand later.