I thought about what the op thought too, million banned accounts could mean hundreds of thousands consoles sold.
MS will definately get more 360's sold but some pirates will definately switch to the competition...just to realize that you can't mod it later. Though I bet majority will just get a new 360 and play offline from now on.
A banned xbox can still play online with a friend, there are dedicated servers and tools you can use to play with your friends without xbox live. System link games only tho...
Regardless, pirates are not going to switch to ps3 as its not piratable format. Buying a new xbox and maybe...holy shit...buying online games? This is what I see happening. My friends are doing it already...