The plans for now are adding more levels, but the idea is to eventually bring it to steam and possibly mobile, too. Ideally I'd want it to be free here, but the steam or mobile version should be a paid one to cover costs at least (a accessible price for everyone, ideally), and also as a means of supporting me.
About the undo suggestion, I'll have to think about it, because the only system this game has to give you a score is the move cout, plus if you reset a level it also resets that back to zero. This was intended so you cold revert back to the original state without being punished for it. And while there is no undo for now, if you click again on the same light that you did last time, it will actually undo that, as it just reverses what you did, in that case. It was also part of the design, thus why I'll have to give it some thought.
I'm glad that you've enjoyed Un-LIT. Make sure to follow me for updates, and thank you for your kind words :)