Couldn't it just be playing with the fact that text describing Newspeak is written in Oldspeak? Pointing to the paradox that the very book would be impossible in Newspeak? More like "we're lucky we're not them" than "and the wolf was shot and they lived happily ever after"? I posit Orwell wanted to keep the book gloomy enough. It was not to be a fairy tale but the warning.
Is there any explicit statement of Oldspeak actually winning in the alternative universe we're reading about? Or the reasons for winning as declared by Ms. Frost ("it's da language")?
Sure--the perspective of the appendix seems open to interpretation, which is great. The very fact he chose such a strange tense, though, leads me to believe he wanted you to at least wonder about such a thing.
I only looked to see whether there was a basis for the claim that it was written from a future in which Ingsoc didn't prevail. There's definitely a basis for that claim in the text. Whether there's a basis for her other claims, I'm not sure--I'd have to read again.
Is there any explicit statement of Oldspeak actually winning in the alternative universe we're reading about? Or the reasons for winning as declared by Ms. Frost ("it's da language")?