You know, re-reading Secret Report 11... I wonder if Luxu is actually referring to himself there in a rhethorical manner.
Observations, Excerpt 1— I have seen it through; the Keyblade War unfolded exactly as written on the Lost Page. Now, the Keyblade the Master entrusted to me must be bequeathed to another. Five Union leaders have been chosen from the surviving Dandelions. I will pass the Keyblade to one of them, and then continue watching the future unfold. Yet it seems that someone has pulled the old switcheroo. One of the Five is an imposter, someone the Master did not choose. They represent a virus in the program he so carefully wrote.
At first, I thought this was meant to be Ven, but it could very well refer to Luxu taking over Brain's body. That would definitely count as a manner of impersonation. Plus, Luxu was not chosen by the MoM, so he fits that requirement as well.
"Someone has pulled the old switcheroo" - It was me all along. Ha!
And we know Luxu is the "traitor" according to the MoM, so he could be considered a virus as well. He's the one that MoM is foreseeing as interfering with his master plan.
The virus has begun a strange undertaking: a reckless plot to allow the Five to escape into another worldline. Surely such a thing can't be possible? We're talking about the same trick that allowed the Dandelions to transfer to other worldlines after the Keyblade War. But these children are no Masters. They haven't the means...unless, of course, a certain lady of magic summoned here from the future knows more than I do.
The use of the arks was expected by MoM, so there's no reason for the Five Union Leaders using them to be considered a "reckless plot". However, Brain was sent forward in time somehow. He did not use an ark, since his memories were kept intact (it was confirmed that the arks erased the user's memories). That probably means that Luxu helped Brain by sending him to the future, dismissing the MoM's orders of not interfering with the Dandelions. Now this would be considered "reckless", since Luxu is doing everything to make sure all the Dandelions he could reach were sent forward in time, directly interfering in their fates.
The Maleficent mention there is relevant because there's one character who actually interacts with both Luxu and Maleficent. That being the Darkness Luxu meets while sending the True Dandelion forward in time in the ark. The Darkness knows about the mechanics of time-traveling, so it's not out of question that Luxu learned how to do so from it (perhaps he overhead the conversation between Maleficent and Darkness?). He has the tools for it, since the No Name could've unlocked Brain's heart and then he sent it forward in time. Brain's empty body was thus left behind for Luxu to put his heart inside.
With that in mind, I wouldn't be surprised if Sigurd is just Luxu again. He has the memories and a belonging of Brain after all. In other words, Luxu found a loophole to keep the Dandelions alive in the future. He sends a Dandelion's heart to the future, takes over the abandoned body, and then acts as the Dandelions' anchor after living through time (in this case, Brain).
It's also no coincidence that Skuld, for example, was found in Radiant Garden, where Braig was working. It's possible that Lauriam, Elrena and Ventus all ended in places Braig/Xigbar visited and left a medium belonging at. We also know that Xigbar directly recruited Marluxia and Larxene into Org XIII, so he knew about their whereabouts. Ventus is the only one that he didn't manage to pick up since Xehanort did it before he had the chance.
The whole Union leader thing was supposed to be by the books. Are these new events just another phase in the Master's grand plan?
I guess here we have Luxu wondering if what he's doing is truly against the MoM's expectations, changing the future, or if it's all according to the MoM's plan. He knows the MoM better than anyone else, so it's not surprising if he thinks that his attempts to change fate are futile.
All in all, this would make the Secret Report 11 a big red herring. Luxu was pretty much just reporting his own actions and using some rhethoric to make it look like he was just observing and not involving himself. Considering how meta Xigbar can get, it would be in-character and very much a twist Nomura would come up with.