I also wanted to add that it's possible there will be some class changes between now and the expansion, but major changes/overhauls are not likely until the expansion.

Overall it isn't that hard to change one thing, the issue is the ripple this will have down the chain. One small change can make a big impact on not just the class, but how well it performs in groups, in PvP, and in PvE so we have to evaluate as many scenarios as possible before making the change live. Based on one change we would want to check out all of the other classes and see what changes they need to keep things balanced too.
Currently we are already working on going through every class in this way, while also adding a bunch of new things because, lets face it, we all like new things.