GATs are a really straightforward extension of what the language already has. All this means is that now a generic type can take a value as a parameter, for example there could be a generic fixed-length array, which took a length as a parameter. In the past libraries had to hack their way around this by having huge tables of types named like, "N1, N2... N16... N1003", which were passed to generic signatures to indicate to the type system how big something had to be.
I don't think this makes the language more confusing, because putting an integer inside of the generics brackets is something that previously you might try to do, if you didn't know it wasn't allowed. In fact, I would go so far as to say that this is a compiler feature, rather than a language feature, because it fills in a semantic hole that already existed in the way Rust programmers thought about Rust types. :-)
I don't think this makes the language more confusing, because putting an integer inside of the generics brackets is something that previously you might try to do, if you didn't know it wasn't allowed. In fact, I would go so far as to say that this is a compiler feature, rather than a language feature, because it fills in a semantic hole that already existed in the way Rust programmers thought about Rust types. :-)