Most successful? Measured in what, money spent? I'm sure other kick-started projects are more successful in that they actually produced a product that resulted in profitability.
As for "not released", they've released a lot more than other projects have. Colossal failures such as Everquest Next have absolutely nothing to show for it - if SC stops development tomorrow (which is unlikely), they have in fact released an early stage game and a ton of near-game content.