You know, I could buy Braga planning Archer to be Future Guy pre-Manny Coto and then switching to the Romulan identity thing to be more consistent with S4/the proposed S5. The big problem with the TCW was that it was forced into the show to give it an even more futuristic element than DS9/VOY while maintaining the ____ of the week story structure, so it never really had any direction and Braga probably threw up his hands and said "Whatever, Archer's Future Guy"; with S4/S5 being "Birth of the Federation," it gave Future Guy some plot context to feed into and Braga could've thought things over and said "You know, if Future Guy was Romulan, this could all make sense."
according to various sources, initially it was not planned who FG was supposed to be, and then later, it was suggested it might be a Romulan. There was never any point where it was going to be Archer. I think it's pretty clear that Braga is pulling this out of his butt years later to get attention and enjoying a laugh about the debate it'll cause.