itch.io

Looking at their patreon, they've got fairly consistent progress logs (most aren't public) going up and are currently working on 0.7.3, so I assume it's just down to slow update times since they can only work on this in their spare time. They've got dev-cycle posts open to the public though, so you can check those if want to see what/when stuff is coming.

Do you have enough storage space? I had an app that gave me the same message when I tried to install it and later realized I had very little storage space left. I cleared some space up, tried installing again and it worked fine. That might not be your problem but it's worth checking.

I'm pretty sure the 'not getting future updates' thing comes from buying it on sale; if I understand correctly, you'llbe able to get it again a little later once they put it on sale again. I bought version .38 on sale for $5.00, and can download the newest 0.46 version without having to pay another $5.

If you pay $10 for the + version, will you then be able to buy the ++ version by paying another $15, or would you have pay the full $25 to get it even though you've already paid $10? 

I ask because I'm interested in the ++ version but I'd rather start with the + version to make sure I actually like the game before going for the more expensive option.