With Model W's existence seemingly all due because of Albert, or so ZX: Advent states, I've speculated else where that Albert more or less is taking credit for minor alterations to what ultimately was coming into existence prior his involvement and without his assistance. Though since Albert got his hands on the 'remains', it is basically into his favor. But I'd like to offer an alternative theory.

Back in Zero 4, during the Ragnarok Incident... Weil, bound to a machine body within regenerative armor, fusing himself with the Core of Ragnarok, Laevatein... Was whole new type of entity. The entire station becoming his body, the Core remaining his place of Consciousness, was still bound to typical Being set-up... Only difference is, Weil was the Core, thus the Station itself was the Body.

When Conflicting with Zero forces his hand to the Fusion, it was within a situation that would have proven in Weil's favor, had Zero not attacked and destroyed the Core. The Core exploding with Weil as part of it, it basically destroyed the Humanoid body of Weil. What there was after Fusion anyway. Then the Atmospheric re-entry destroyed nearly every critical part of Ragnarok... Leaving Laevatein more vulnerable to impact. Not to say the atmosphere burning didn't have an effect on the Core, it just didn't take enough to have been reduced to nothing.

This event occurred during the Human portion of Alberts life, at least the early portion. With that speculation, Albert would have had some knowledge within Reploid basis and technology. Locating and obtaining the remains of Weil's Laevatein, Albert would have the medium that would ultimately come to shape the future that is ZX.

However, the Laevatein remains had Weil fused within them. Meaning, Weil's body is gone, however he continued to exist within the remains. If there is any extent for his body ability too fused is unknown. Though for the sake of this theory, it exists. To the point that Laevatein would eventually begin to reform. Forming a Composite body of Weil essentially. So even without Albert, the MegaMan Universe would have seen Weil again... In some form or another...

But because Albert got to the remains first, he was able to study the remains and reconfigure it into what he dubbed as Model W. Which would go on to be re-buried, re-uncovered, and led to the Ciel 6 and Model A... Thus setting the ZX events up.

The ZX series would have been very different had Albert not intervened with Laevatein remains. There may not have been the Ciel 6 (that we would have seen, or in the same fashion), no Grey nor Model A (that we would have known)... Instead, it would have set forth another future... Something similar to Ghost in the Shell. With such a threat as Weil continuing to exist, with no Hero's... Someone (Ciel, Allouette?) would have possibly uncovered the Hero Cyber Elf's again... But would most likely have implanted such into newly crafted bodies. It would have essentially been the Hero's Resurrection, not as a BioMetal...

Ciel did create Copy X, who was nearly identical to X. So the others wouldn't have been far fetched. And taking ZX's adaptation of Allouette, Prairie... She would have shown interest in the same, or would have opted to assist Ciel, her older sister. It would have been a team effort, more or less.

This is to review what Sigma has went through near the current latest installment in the X series.

At the end of X7, Sigma was shown to have been ejected from a Building, several stories up... Not to be shown again... Then we see in X8 a Sigma entity without anything of that body? No head, or body similarities.

This is where my theory comes from. Sigma manipulated Red Alert in X7, with most fighting the Hunters. Yet we can assume that few survived. But mostly we can assume that Sigma survived (obviously, but not the point) and from then disappeared.

My theory consists of Sigma going into hiding after the X7 events, and either using remaining Red Alert members as a cult to his aid, or other members whom perhaps have been following him for years. What I mean is, looking at the inconsistency of information after X7 to the full blown 'information' present within X8, something may not be flowing straight up.

After he was ejected from the building, his injured body would have sustained impact damage. But his core, his Head was still in okay condition. Which without the heads destruction, the Virus cannot be destroyed in that degree. So, Sigma survived, but with his followers, manipulated or whatever, taking his damaged body and/or head into hiding. To which where Sigma was projected into a machine that would keep the head alive. From this, we can also suspect that his dreams would still be of priority, but without a new body presently, he was unable to act.

So instead of Sigma taking over yet another body, what if Sigma's Virus was granted a Proxy sort to say, and a copy was created with the same potential with the Virus? And that Proxy was the Belial Sigma found in X8?

It would make sense for Sigma to ruse the Hunters into believing that he is gone. It gives Sigma another puppet to act on his behalf. And it furthers his grip on what is going on around him. Plus it is an overlooked possibility, other than another character granting Sigma a full DNA resurrection...

Many reasons I say this is because of the character inconsistencies between Sigma in X1-7 and X8. Plus the copy Sigma's in completely different forms. Perhaps it is that body Sigma resides in within X8, but it is Belial Sigma (proxy Sigma) that was seen as the villain.