Naturally, the 31-point Shadow Dance is totally inaccessible to Rogues speccing other trees. But what about Shadowstep? Is that a tree-specific, unpointed talent that is totally inaccessible to all other specs?
Inaccessible. Shadowstep is essentially no longer a talent. There is nowhere to buy it. You don’t get any passive bonuses for picking your second tree. Essentially you choose at level 10 whether to be an Assassination, Combat or Subtlety rogue, and while you can change your mind later, that determines what special ability and what passives you get. (Source)