LGTM. I support enablement (provided it is auto-fixed) of requiring trailing commas in multi-line arrays.
I find it valuable to remove a choice that shouldn't carry any meaning in the first place (namely, the presence or absence of a trailing comma). Specifically, the choice to prefer presence (instead of absence) of trailing commas I believe improves diffs, as well as eases refactoring when re-ordering or copying code from one place to another.
With regard to Thiemo's point, about communicating the significance of a final item through absence of a trailing comma: I do not consider the presence or absence of a comma to be effective communication between developers. I think this is too subtle. When code has a limited-length return value, it should be described in its doc block, and/or covered by strictly asserting unit test, and/or typed with value shape to Phan, or if otherwise important through an inline comment. See also: omitting the (technically optional) semi-colon after the last property of a CSS rule, or after the last statement in a JavaScript function.
We can either: make the trailing symbol redundantly reflect a pre-existing semantic and train ourselves to remember to type that correctly — or, — we can make it a consistent part of mental boilerplate and remove the part of our brain that will draw attention to this detail every time we read a line of code to determine whether and what it could or should mean.