Depending on if the monk info is good on Monday I don't see why not to try and become the best at a new class. I have mastered the DK to all it's potential. I have loved my DK and we have had a good run, but it looks like the monk is going to an a lot more fun class to play.
The big thing for me about changing classes was that I would lose all my achievements/mounts/mini pets etc. Now that all of that is going to be account wide I don't have to worry about moving to another class as my main. Though I will have to change my sig from best dk in the world to best monk in the world. I plan to learn everything about the monk and maximize its potential.
What about you guys?