Squigles, I do grant that you have a point with them being taken by surprise. I only pointed that out because Itachi is both clever and paranoid, something that leads to him planning very far ahead. Your idea about Itachi trying to draw Kabuto closer might be true, but somehow - call it a hunch - I feel that it was just surprise or some other problem.
Right now, the level of Kabuto's power and the depth of his techniques is clearly unknown. We've seen Edo Tensei, we've seen Dragon Sage mode. We've seen him expertly use medical jutsu in a way that rivals any other ninja known in the naruto world.
I've always said Kabuto is one of the most powerful ninja in the series, simply because he's always been very skilled and resourceful. I wouldn't be surprised if he's got even more up his sleeve, and really gives Itachi and Sasuke a run for their money.
In that sense, I wouldn't be shocked to see more 'surprises.'
You brought up an excellent point about un-summoning individuals. I'm not sure he can do that, since there is no data, but it does seem likely since he can summon individuals. Is it the Genjutsu? Is it Kabuto's desire for a challenge, to foolishly prove his superiority and might? Villains often do such stupid things when they could theoretically win. I don't know, but given the flashback, it seems plausible.
Edo Tensei is a summoning technique which brings the soul of the person back from the dead, into a new vessel that was prepared just for that person. So far, we've seen Kabuto summon individuals, small groups, and large groups of people using Edo Tensei. We've seen him unsummon individuals (deidara), and we've seen him exert a precise level of control over each individual person.
Some of them have been mindless slaves sent to simply kill others. Some of them have been left with a little of their prior knowledge and humanity, capable of making some decisions, but mostly still being forced to obey Kabuto. Then there are a few specific ones who have been given free reign over their actions, like Madara.
If Kabuto can summon so many people using Edo Tensei, control each one of them on specific individual levels, and decide what level of control to use for each individual one, then it's only natural to conclude that he can also summon/unsummon them individually.
Which means that logically, if Kabuto was able to unsummon Itachi, then that would have been the best course of action as soon as he was put under Shisui's genjutsu. As a result of Shisui's genjutsu, Kabuto lost Nagato as an Edo Tensei, which was one of the more powerful ones he was able to summon, aside from Madara.
So yeah, if it were an option, he would have exercised it by now, since he's obviously more than capable of doing so.
You mentioned the possibility of Izanami already being in effect. I theorize that the activation of the jutsu or the ending of the jutsu might be the cause for Itachi getting hurt. I base this on the fact that Itachi's right eye was closed (Is it from pain or due to losing a Sharingan to Izanami) right before he regenerated, sharingan included. It's impressive if he managed to save Sasuke under those conditions. This begs two questions:
1. Was the Izanami in effect, based on the above? Is my observation at least accurate, even if my interpretation is wrong?
2. Will the Sharingan regenerated by the Edo Tensei after the use of Izanami be of any use?
3. Was Sasuke distracted for some really important reason? Why did Itachi tell him to stick close?
4. Is it certain that one will lose eyesight after the Izanami? Do we have cold hard facts? If not, will there be another sacrifice or no sacrifice at all?
Itachi's right eye wasn't 'closed,' it was blacked out, like it was an empty socket. Basically a result of the reanimation effect of edo tensei, his eye just hadn't come back yet. Also, the side effect of Izanagi isn't that the eye just loses it's sight, it's that it becomes sealed, like if someone had used a sealing jutsu on it. That's not something that can be undone or reversed by Edo Tensei, I don't think.
As far as Izanami goes, I don't think it's been used yet, all we've seen is that 'it's ready.' My earlier post was just to indicate that Itachi had the technique prepped and ready to go, and was just waiting for the opportunity to use it.
I'm pretty certain that Izanami will carry the same side effects as Izanagi.
NarutoMinato raised a rather interesting point about the Amaterasu, one which I'd asked myself. I'm glad that you pointed out the use of the Susano'o squigles, because I hadn't realized the significance of it, even though the difference was clear in the examples I brought up. This brings up the following questions:
1. While the EMS provably returns the eyesight of the person in question, does it really protect one from all MS techniques? Could the use of Amaterasu cause further damage to the EMS where the Susano'o doesn't?
2. Are there other EMS techniques that cause bleeding or loss of vision?
3. Why is the case of using Amaterasu through the susano'o (Blaze release Magatama and Amaterasu coated arrows) different?
I don't think his eye bleeding has anything to do with MS or EMS. I think it has everything to do with just that one technique. For some reason Kishi decided that it would cause the user's eye to bleed, but not all the time. I also don't think that once the user has EMS, that any techniques used would cause blindness.
I theorized earlier that the EMS might still cause blindness due to some techniques or pose another risk. (Most high level techniques in Kishi's world pose a risk and are not risk free, afaik.) Was it due to this that Madara sought out the power of Hashirama (life force and healing from the Mokuton to restore his eyes) and did he really gain a bit of Hashirama's power? Did that cause the evolution of the Rinnegan? I know that this theory is a bit wild, but it is possible to some extent. In any case, I'm curious.
Basically, both the Uchiha and the Senju were given the power to control the Bijuu. I believe that the only Senju so far who's been able to control the Bijuu on the same level as an Uchiha, since the So6P, has been Hashirama, due to his wood element release.
I think that Madara discovered his ability to control the Bijuu with his Sharingan, but realized that Wood Element release could trump his control, and that the only true way to control the Bijuu, was to combine the Wood Element with the Sharingan, which is what we saw Danzou attempt to do.
I don't believe that Hashirama's DNA had anything to do with Izanagi, Izanami, or the Rinnegan. I'm fairly certain that when Madara acquired Hashirama's DNA, it wasn't an immediate power up like an episode of DBZ. It was more along the lines of 'I got his DNA, back to the lab to experiment' and he was only able to use it's power long after the fight.
We know that there's a lot more to the story than what we've been told, and I highly doubt that the fight and other events played out like many of these other fans think they did.
Finally, I'd like to point out that Kabuto called himself closer to the Sage of the Six Path's than anyone else. This suggests to me that he might have made further body modifications. However, it could be because he gave life through the Muki Tensei. Thoughts everyone?
I think it's absolutely possible that Kabuto made numerous other body modifications. He's sitting here basking in his 'infinite power' while bragging about using Hashirama's DNA to complete Edo Madara to beyond what he was in his prime.
What's to stop Kabuto from using Hashirama's DNA on himself? All he needs is a big enough boner for the idea, and it's as good as done.