Agreed, the ultimatum was uncompliable because Austrians had the guarantee of the Germans that they were locked. As MC points out this puts the cards in Russias hand, do they balk, or do they fight. Again the Russians were not ready then, but the Germans felt that they would be ready soon and better hit now then later. So what started as the third balkan wars turned into WW1 when Russia mobilized.
IMO, WW1 would have happened no matter what. The Brittish did everything they could to divert the war, but it would not happen. Furthermore, while Germany was building a Navy to contend with the Brittish fleet, had they known that the Brittish were to unconditionally join the entente, then that would have delayed things.
@MC, as far as the medieval land with the monarchy, the ottomans were worse... But I guess thats not either here nor there.