<> are the worst characters for generics, except for all the others that have been tried. () leads to the type syntax being difficult to distinguish from value syntax, which is great in dependently-typed languages but bad elsewhere. [] is already used for slices, albeit in a different way; and C should be objection enough if you want to make types look like values. {} is a nonstarter because it leads to ambiguity between return type and function body, and in an everything-is-an-expression language, once again we are back at types-look-like-values. There are no more matched pairs left on an ANSI keyboard.
Personally, while I hear you that :: is ugly, I do really like being able to distinguish module paths from value paths at a glance. And when looking for an alternative, we once again run into other characters already having far more familiar conflicting uses, or just being too weird. (E.g., # or @ could have been used, but that's probably worse than ::.)
I'd say that because of everything-is-an-expression, and items (e.g. functions, type definitions) allowed in block scope, rustc will accept exceptionally opaque syntax compared to other languages.
But that doesn't mean that you should be writing exceptionally opaque syntax. For example, in the given example, I would demand that <T: AsRef<Path>> be written with a where clause instead. rustc will accept either, but humans should demand `where` at least whenever the traits contain `<>`.
> It is sometimes quite useful in practice to recognize that two isomorphic objects are not literally the same. So I am skeptical of any approach that wants to blur those distinctions.
This paragraph betrays that you have not done much work at all with HoTT. Type theory would be inconsistent if distinguishable objects could be substituted. It is not accurate to say that they are treated as "literally the same". Indeed the whole point of HoTT is that substitutive equality is not the only useful kind.
Dang explicitly bans people for posting things which are too damaging to left-wing politicians.
Just today he explicitly editorialized a post title (with a comment explaining why) because it exposed some government corruption; I don't even remember what because it was just so unremarkable and ordinary for HN. ETA: Oh lol it was the same subject as this post, but different title. I guess he let this one get away from him.