With Shadow Step and Preparation (both Subtletly skills) becoming baseline I can't think of a reason anyone would choose Subtlety over Assassination.
Assassination's Poison damage ignoring armor completely seems to squash "Find Weakness," and the lack of positional requirement also seems as though it would dramatically give Assassination the edge?
Can someone with a bit better reasoning, and cognitive skills explain this to me? I know that MoP is a few months away, but the servers are down and I wouldn't mind having a discussion about this with other Rogues as the subject interests me. :-)