Atom did this with the backing of a very well-financed company, and it still doesn't fare all that well with niche languages.

I agree with the general gist of your first post, but I think it's important to recognize that unless you can build on some portable standard method for defining editor support for programming languages, there is going to be a cost to living in the niche; it is going to make you more hesitant to experiment with new languages. (This is speaking as someone who has also implemented their own Lua-based text editor.)