I've done similar work (cross-platform toolkit) so I know that it is not trivial but doable. Sublime HQ is not a big company, if they can do it most companies

I've done similar work (cross-platform toolkit) so I know that it is not trivial but doable. Sublime HQ is not a big company, if they can do it most companies can. I am pretty sure they are enjoying the payoff of the early decision of going cross-platform and using their own custom built toolkit. Also, you don't have to do everything from scratch, libraries like glfw are well maintained and can help a lot.