When you have an "amp-carousel" there is no way to start that carousel at a point other than element 1 in the list.

Why might this be useful?

I have a list of images and they relate to dates current/past and future - it would be useful to start with "today" shown and centre and allow people to scroll back (into the past) of forward into the future.

I see this most useful in the carousel format where you have a selection of images and on different displays you might see one, three, five images as the display device gets wider but the default is the center and you can move back / forward through the images rather than starting at 1 and moving forward only.