Okay the speech change thing. I really don't see why its a problem. Generally changing environment results in slight change in the way people talk, or accent. I've seen it more than once in people who've gone abroad for any significant period of time. Such a change is actually addressed directly by some Guados in FFX.
To say that it isn't hinted at is unfair. Some of Edea and Rinoa's lines in Edea's house show very strong foreshadowing,as if I remember correctly, does a scene where you see white feathers turn black, though I can't remember much about that. Though if the writers didn't intend R=U at all, these lose most of their force. Griever on the other hand is quite a big pointer. It's a symbol that only really connects to Squall and Rinoa, and I still think the intimidation explanation is just pointless.
The game does leave holes in its plotline that people fill in or work out. Squall's parents and history being a fairly simple example. The gap between the 'present' and Ultimecia's time is not hugely delved into, and it is not uncommon in stories involving time-travel for persons to meet themselves. It is creative filling yes, and Ultimania is a massive problem, but to completely dismiss R=U without it is in my opinion unjustified.
Oh, and I forgot about the fact that GFs induce memory loss in my earlier explanation of why Rinoa couldn't remember Squall and co.
