I think Valve needs to have a contractual system in place for SEA, whereby developers are required to finish the game in 'X' amount of time, or forfeit a huge chunk of their profits. Failing to deliver a final game (not just an incomplete game marked as final) would potentially also be grounds for blocking said developer/publisher from SEA in the future. That would resolve a number of issues with early access.
As a third party vendor I don't think Steam have the right to stipulate a SLA agreement like that.
Eg you order something from the Store, the Store says that they will have to order from the Manufacturer and that the Manufacturer expects delivery date to be 2 weeks. Your something doesn't arrive in time. The Store can refund you and cancel the order, but they can't force the Manufacturer to do anything.
