Is this true? The liberalizations I've seen (trailing comma in calls, leading vert in arms, trailing + in bounds, ...) all seem to be aiming for a different philosophy: All items in a sequence can be written the same way, if you so wish, with no need to do something different a particular position. Thus foo(a, b,), T: A+ B+, |A |B =>, ...
That serves both the code generators wanting to just do the same transformation for each item as well as the rustfmt principle to prefer formats that result in minimal diffs in source control.
That's very different from supporting different formats because people have different tastes.