Until someone comes up with hard facts that Ultimecia IS Rinoa, then I won't believe it. It's all well and good saying "This is a big pointer or this is a symbol towards this case"

Until someone can actually get something from the game which links Ulti to Rinoa in anyway stronger than "there are plotholes" I'll maybe give the theory some thought. Unlikely though seeing as there is a guide which says a soceress has a normal human life span, but oh no, we know more than the game creators.
I mean you could just as easily say that Irvine is a girl since he has long hair.