I'm wondering if such a classification has been discussed before or is it mostly original research?

Original research.

I think it's pretty rare to read what I'd consider to be unambiguous attitude statements here on LW. I guess it might be worthwhile to call them out when they happen.

"None of them are falsifiable claims about the nature of reality."

Hm. Well, in the post, I argued that the attitude/fact distinction is in the head of the speaker. Which means that my attitude statement examples are examples of the kind of things people say when they make attitude statements, not attitude statements themselves. So I guess maybe you'd have to find someone who endorsed the claims and ask them if there's any empirical evidence that would change their mind, or something like that. (But what if the Atlas Shrugged person says yes, if I read a better book, I would change my mind?)

BTW, I'm not sure how to deal with mathematical truth, so I didn't mention it.