Brilliant idea!! If you can pull it off, that is. Imagine an organized strike at 1 million difficulty.
You'll be solving one block every 10 hours and it would take months for the next difficulty drop.
That actually sounds like it could be a real vulnerability if anyone really WERE to organize enough miners... Has anyone addressed this? Should the system change difficulty primarily in N blocks but have a secondary failsafe to change difficulty every N days if the block limit isn't reached? Now that I've got this thought in my head it legitimately worries me...