The game has been in development for many, many years now. My guess is Alex will put it on steam once he hits 1.0, which makes sense.
The main thing here is that if he had tried to put this on steam when he first released it then it would have faded into obscurity even though he's been updating it all this time. You can see how people take to significant changes by looking at Stellaris. There's plenty of people complaining about that game no longer being what they originally bought which, while I admit to be an understandable criticism, isn't one that truly makes sense to me. I mention this because at the very least the next version will include a redesign of the skill tree (as seen in the last blog post). Better to finish all the big changes so he can mark it as a largely-finished game rather than have to post it under Early Access or Development tags- which would likely turn off many potential customers.
TL;DR I think Alex should continue with his plan of "When it is ready", as MesoTroniK said.
Otherwise though, welcome to the forum and hope you're enjoying the game!