I cannot see how any rogue would not want additional sneak attack damage, so taking some assassin enhancements seems necessary.
you don't get sneak attack if you have aggro, and i cannot imagine any rogue build on live that does not include melee threat reduction.
self-healing for rogues depends on using heal scrolls, which at high level only heal enough if you take wand and scroll mastery.
These three are in three separate trees. so, essentially, why multiclass?
I love playing my assassin/ninja spy build on live. I was excited to unlock drow racial tempest enhancements for him. But i cannot have even close to what i currently have with these critical enhancements spread out among the three trees. If the most basic (IMO) and important rogue abilities require all three trees, the rogue multiclasses seem to me to be dead. I hope a dev reads this or my rogue enhancement survey response and reconsiders the way this is set up.
If you agree, or respectfully disagree, please comment. I am pretty bummed that one of my favorite toons to play seems like he will be totally borked with this new system.