This seems like a great idea! I am a little wary though, like others have said what guarantee do we have that the game will continue its development? I know this is what Minecraft did and it worked fantastically (I bought alpha Minecraft, and have been playing it ever since). But what are the chances every game is going to take off like Minecraft. I can still remember all the Half-Life/Half-Life 2 mods that had awesome ideas, put out an alpha and then never went anywhere, true most of this had to do with lack of funding, but still there were hundreds that didn't go anywhere for every one that made it to a semi-playable state.
Some of the games do look good though, Kerbal Space Program looks hella-fun (how is it from people who have played it?). Kenshi looks intriguing, but also looks like it's in incredibly early alpha. Prison Architect is a neat idea, and their steam promo video is hilarious and points out that it is an alpha version of a game, and points out some hilarious bugs that apparently exist.
The prices on them seem a bit steep for an alpha build of a game too. $20 for an alpha version of a game that may go nowhere? No thanks, not yet at least. Doubt I will pay for any of them quite yet, but will definitely keep a close eye on them.