I predict that Sai's mission will become brutaly clear in the next chapter, although I can't tell you what it is. Im sure we will get a definative answer nex issue.
Also, I guess Sasuke makes his appearance next week. This arc is at its climax so its perfect timing. If no sasuke then Yamato will get to Naruto or Orochimaru will leave. I can't see this thing going much further than it has already.