Well, I am going to plus rep you for this well thought out theory. You have backed up your claim with sufficient evidence, and now that I think about it, it makes perfect sense. How dull would it be for all Uchiha who achieve ms to have the same ability? Also, from what we have seen, almost all Uchiha who have unlocked ms have had different abilities, though we haven't seen many.
Lets look, Shishui unlocked a unique ability to him, Kotoamatsukami. I am going to assume he died before he was able to unlock his second ability and Sasunoo. No one but Sasuke and Itachi have been shown to use Amaterasu, this should be the first indicator. Sasuke used Amaterasu, but he is Itachi's brother, so it could mean that this ability was genetic, or that when Itachi put the fail safe against Tobi in him, he inevitably inherited the ability.
The debate here is weather Sasuke's Enton: Kagutsuchi is his second ms ability, and it also makes perfect sense that it is. Tsukiyomi is a technique that is supposed to manipulate time and space, that is what defines Tsukiyomi as a technique, Sasuke cannot do that with his genjutsu, therefore I come to the conclusion that he cannot use Tsukiyomi. He can do things with Amaterasu Itachi never dreamed he could do, and if you put two and two together, it was right after Sasuke discovered his ability to manipulate the flames that he unlocked Sasunoo.
This is just my two sense, I believe that you need two ms abilities to unlock Sasunoo, and it doesn't have to be Tsukiyomi and Amaterasu. So in conclusion, until proven otherwise, I do not believe Sasuke has Tsukiyomi.
One more thing, for people saying that his version is weak and are using the databook, it clearly says in the databook that the user must have complete master over both techniques to be able to unlock Sasunoo......if that is true, we already know that IF Sasuke has Tsukiyomi, then he definitely has not mastered it, so how does he have Sasunoo? Just a thought.