Have there been serious attempts to widely teach musical literacy?
To answer: Yes, they included learning notation, in fact that was the point.
And they included learning music theory in the same sense learning spelling to first graders includes grammar. Just because it's not explicitly described in terms from the theoretical model, doesn't mean it's not there.
They did however firmly link music note to finger positions, and I think that's a big part of why they failed in promoting universal musical literacy (even though professional musicians too typically sight read that way).
But not enough to become truly literate I'd say. But still, it was definitely part of the curriculum.
I was in grade school in the 70's, but I certainly did not. We had "music" class, which was mostly learning songs to sing and basic instruments, but those were more a "put finger here, then here, then here" type of thing. From 4'th grade+ we had optional band (which I was in), so I learned some there.
But not part of a standard curriculum.