Yes, I am not entirely sure yet what would be the best user interface for this yet, but animation loops are a must!
Note that currently, it is already possible (though very clunky) to achieve something similar. Suppose you want to copy all the frames 1,2,3,4 into 5,6,7,8. You can do this:
- On frame 1, use the rectangle of selection to select everything on frame 1.
- On frame 2, hold "Shift" and use the rectangle of selection to select everything on frame 2, without losing the selection on frame 1.
- Repeat for frame 3 and 4.
- Go back to frame 1, and hit "Ctrl+C" (copy)
- Go to frame 5, and hit "Ctrl+V" (paste)