Frankly, I think Keldar has it in one.
In order to nix the class, a DM would have to engage in some pretty hypocritical semantic dickery. First he'd have to claim that, by the letter of the rules, Changeling doesn't qualify, since by the letter of the rules they don't qualify for the 3.0 Quick Change--despite the fact that they'd likely qualify for an updated version of the same feat.
Then he has to turn around and say that, while by the letter of the rules the 3.5 Quick Change feat supplants the 3.0 and should qualify the Changeling for the PrC, the intent of the rules wasn't for those two feats to be the same.
At that point, he might as well just invoke "No, because you can't have nice things."