I love expansions, and not just for new content. Large-scale changes to mechanics make the game seem new and fresh as opposed to the same old thing with new zones and different bosses.
This one took me by surprise, though. Blizzard has long been saying that they wanted to get rid of extraneous talents in the trees, and they especially want to remove the “boring” talents. In order to decrease the bloat and streamline the talent trees, they announced that they are shrinking the trees.
Instead of 30 or so talents in each tree, there will be around 20. Instead of getting a new talent point to spend every level after 10, you’ll now get a new talent point to spend every other level. The top talent in each tree will be 31 points instead of the current 51.
All that is fine with me. I agree that the talent trees could use some pruning.
The part that concerns me is that once you spend a point in a tree, you cannot spend any points in any other trees until you have 31 points in your primary tree. That would happen at level 70.
For rogues, that means that if you choose to spec into Assassination (for example) when you are level 10, you will have to put all of your points in the Assassination tree until you hit level 70.
Now, we have absolutely no idea how the trees will look. This concept has been proposed by Blizzard, but not yet implemented in the beta. The talent trees that we were shown a month ago are now going to be thrown into the scrap heap and rebuilt from scratch.
Here’s my concern. Lets take a talent like Dual Wield Specialization. This is in the combat tree, yet there are absolutely no rogue builds of any kind without 5 points in this talent. It is a major contributor to our damage. Without access to this talent, any Assassination or Subtlety rogues could be disadvantaged for the first 70 levels.
Maybe this is a pointless concern. Most rogues level as Combat spec, so this concern applies only to the few who level as other specs. Of course, you can always respec as desired. And we know that Blizzard can use the new passive talent tree bonuses as tweaks to balance damage across the three specs.
Still, I’m sure that there are many examples of talents for other classes that are “must-have” across all three specs. I’m holding my breath until the new talent trees are revealed to see how this plays out.
Forever a Noob - A WoW Rogue Blog 
They’ve said the the majority of the talents they’re looking to get rid of are the ones no one takes or the ones everyone takes. If pretty much everyone takes DWS, it’s likely to be removed altogether and either reapplied some other way (Training, Class Default Mechanic) or just go away altogether.
With a major overall to everything, I’m pretty sure talents like DWS are just going to become class traits or that the need for them will be removed to begin with.
I believe there will be key abilities available for each tree, for instance if you decide to go assassination at level 10 you will gain the ability “Mutilate” wich will make a big difference. Indeed dual wield mastery will probably be a trait of the combat tree, not so much a talent.
I have full confidence in Blizzard that they will keep the balance of the game in mind. Also they have said that they want more rogues to use daggers 🙂