From what I can tell, it hasn't been done with Flexbox alone. To get the order right, you have to specify a fixed height for each element, making it non-responsive at best. I am wondering if grid somehow helps.

There is also of course the order property, which with some cleverness can re-order elements from 1, 2, 3, 4, 5, 6 to 1, 4, 2, 5, 3, 6. You'd have to get awful clever with it though to figure out how to do this right, so still might rely on JS.