I suppose it could still be added in the future; there are probably several syntax options that would be fully backward-compatible, without even needing a new Rust edition.
Sorry, I don't agree.
First, code is read far more often than written. The few seconds it takes to type out the arguments are paid again and again each time you have to read it.
Second, this is one of the few things that autocomplete is really good at.
Third, almost everybody configures their IDE to display the names anyway. So, you might as well put them into the source code so people reading the code without an IDE gain the benefit, too.
Finally, yes, they are redundant. That's the point. If the upstream changes something and renames the argument without changing the type I probably want to review it anyway.
String(repeating: "foo", count: 42);
String(cString: zeroTerminatedBuffer);
String(42, radix: 16);
String(contentsOfFile: "foo.txt", encoding: .utf8);