The demo is now available on the Steam store page! It is updated to 0.6.4d which only contains small changes compared to the last Windows version on Itch.IO.
Word of warning that this version has a bug related to the in-game achievements. They will not unlock unless you you start the game for the second time, as the new achievement save file cannot unlock new achievements.
0.7.0d will be releasing soon with much more content, as well as fixes and optimizations so the game can run even faster on low end hardware!