As someone who has been and still is working on one of my own for many years now (and at this point it's far even from his efforts), I think having the time to do it is the biggest challenge.

Yes. With me it's motivation and energy. I'm not forcing it though. This is for me and it's currently solo project so I don't feel pressure to ever get it off and complete it. It's still worth it because I really enjoy doing it.

Maybe you could continue developing Kosmonaut? https://github.com/twilco/kosmonaut