Well, the problem is, the remaining bits of code from Kobo Deluxe/XKobo need to be replaced for legal reasons, before a Steam release is possible. This is code that desperately needs to be refactored or rewritten anyway, so it's no major setback, but the legal situation prevents me from even entering Steam Early Access until this is sorted.
Meanwhile, I took a ~2 year break from "spare time" coding, and then, 2020 has been... interesting. However, over the last few months, I've been updating the sound engine and other related projects - and next up is a new graphics/game engine core, which is pretty much the blocker for Steam.
So, Steam Early Access in 2020 is a possibility. There will likely be a content update, including a new soundtrack, before, or in conjunction with that.