I don't know enough about client implementations to say whether it is unsaveable, but let's say it is: why would 308 exist? That suggests the HTTP spec folks believe it's fundamentally changed meaning. With new-301, new-302/303, 307 and 308, we'd cover each of the 4 cases. Seems to strongly suggested that's necessary.
You can't just "let's say" 301 is unsaveable, because that's the only outside fact that determines whether TFA's argument is correct. You seem to be assuming that the committee's decision is evidence that it's a good idea, which is exactly what TFA is trying to determine.
Meanwhile, hobohacker got around to answering the real question.
