I'm not saying the input should accept all possible formats. It's tempting but the example you've provided makes it impossible.

What I'm saying instead is, that we can recognize the default user browser date format (that is set on the operating system level). With that information we can display that format next to an input field and expect the date provided to conform to that format.

As the idea evolves, we could also make it possible to change the expected format on the input, form or user account level.