I think that Itachi set Kabuto's "fate" to be that he has to kill Itachi to get out of the loop. But since Itachi is an Edo, Kabuto CAN'T kill him, so the only way that Kabuto can get out of the loop is to release Edo, therefore "killing" Itachi.
Basically the same idea behind your theory, but I like that one a little bit better, makes more sense than just Itachi setting Kabuto's fate as ending Edo.
Also, that plays in nicely with Itachi saying chapters ago that Itachi himself is the weakness of Edo Tensei. Which is amazingly perfectly true. Itachi knew all along that Izanami was the only way to beat Kabuto, and that Izanami would really only work if he himself was an Edo Tensei. So Itachi saying that Edo Tensei's weakness is Itachi as an Edo...If Itachi was not an Edo, Izanami would not work as well since if Itachi wouldn't be able to get stabbed so many times in the loop and regenerate, but since he IS an Edo, the loop works out perfect. I don't know, just blows my mind.
Edit: Oh and to everyone saying why doesn't Kabuto just recast edo after releasing it. It is not that easy. Kabuto completely releasing Edo is NOT just say Edo Madara going into his coffin and getting sent away, or Itachi getting put into a coffin and getting sent away. Kabuto releasing Edo would mean that the SOUL would stop being bound to the living person that is it being bound to, and going back to the Pure World. Which means that Kabuto would need to first find more living sacrifices to bind the soul to, AND most likely get more of the DNA of that person he wants to bring back to the Impure World. So he would have to go find more DNA of Madara, and Muu, and Itachi if he wants to bring Itachi back. THEN go find 3 more living sacrifices to bind the DNA onto, then do the whole ritual that he showed Tobi. THEN he would have his Edo's back. It is just just simply him casting it again and more coffins show up.