This is probably the law student in me talking, for which I wholly apologize, but....

It seems to me that the burden of proof here rests on the R=U crowd. Its not alluded to in the game in any meaningful way, unless you are looking for that answer and working backwards to support it.

Personally, I agree with the premise that sorceresses are not immortal, and that Ultimeca is very far into the future. Remember Odine's description of the machine that allowed her to transfer her conciousness.