I just checked in iMessage. When you add an attachment and select photos, you get the same picker that the rest of the OS uses, it's just in a collapsed state.

I just checked in iMessage. When you add an attachment and select photos, you get the same picker that the rest of the OS uses, it's just in a collapsed state. If you swipe up, it'll expand to fill the screen and that same "Location is included" label and configuration menu is available.