it always seemed to me that Lucas' original intent was that Sidious knew Anakin would eventually surpass him and if he did, the pride would be in taking the Jedis chosen one and corrupting him into being the most powerful Sith Lord ever. He says to Yoda that "Darth Vader will become more powerful that either of us" I always took that to mean that Sidious knew his fate would be to die at Anakins hand one day