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According to this posting on Giant Bomb http://www.giantbomb.com/articles/steam-updates-early-access-rules-guidelines-for-de/1100-5101/ Steam have updated the rules/guidelines for early access.
Don't launch in Early Access without a playable game.
If you have a tech demo, but not much gameplay yet, then itâ€™s probably too early to launch in Early Access. If you are trying to test out a concept and haven't yet figured out what players are going to do in your game that makes it fun, then it's probably too early. You might want to start by giving out keys to select fans and getting input from a smaller and focused group of users before you post your title to Early Access. At a bare minimum, you will need a video that shows in-game gameplay of what it looks like to play the game. Even if you are asking customers for feedback on changing the gameplay, customers need something to start with in order to give informed feedback and suggestions.
Seems some what contradictory, on the one hand they are saying don't use early access without a playable game but then go on to say you can get away with a video.