Is six months an extensive amount of time? Makes me think of this.
I think that it depends on who is getting the game and for what purpose. Alpha testing to a few people who will try to break the game and know how to write a descent bug report makes sense. Alpha testing to everyone doesn’t as it is likely to slow down the development process. I’d rather have a decently completed game in six months than some barely completed mechanics right now and have to wait till sometime next year to get what I would have got in December because sorting through all the bug reports and dealing with the “This game is so buggy!” crowd impeded the game development.
I think basic survival should be the minimum of the earliest release. Crafting. Building. Resource gathering. Building can be basic. Slap down some sections of prefab flooring and some prefab walls. Resources can be few. Wood, maybe some stone, and something edible. Crafting can be simple to non-existent at first. As long as the players understand that bugfixes and updates might break a game in progress (a la Mincraft minecarts), I think they might be satisfied with less than complete game mechanics.
I think if you had a solid building experience (perhaps a little bit more than what is in the prototype video) then people would be satisfied to get building and wait as more content develops. The danger is that if the first release only has building, there will be cries of “Minecraft Clone!!11!” from the unwashed masses because then it really won’t have more than Minecraft at the time.
Whatever you release before December, please don’t let it prevent you from fulfilling the promises you made in your Kickstarter campaign for the rest of us who are willing to wait six months for this gem you are making.