The new source engine is relevant to Portal 2, but like bustapr said, and I have to agree, the new engine won't be bigger than the Portal game, so if its not Portal 2, and its not Half Life 2: Episode 3, then it has to be Half Life 3 (with source engine 2). If this is the case then its safe to assume Portal 2 will be using the new engine, and they may even tell us about L4D3 and TF3.