the timeline widget contains tabs corresponding to different frame tags. each tab displays the same timeline but differently.
you start with a default tab corresponding to the animation that's gonna play when you press Enter.
then you select some cells on one or more layers (or frames if you're selecting from all the layers) and press F2 to create a new frame tag. this will create a new tab for that tag.
on each tab created this way all unrelated cells and layers are greyed out.
on the default tab all the cells that belong to a frame tag are (possibly) colorcoded and trying to change them causes a switch to the corresponding tab. since all the tabs display the same timeline the switch shouldn't be too disorienting.
ultimately as you move all separate animations into individual tabs the default tab becomes a map of your entire composite animation.
again, this is a very rough idea but i hope it makes it easier to create the kind of composite animation i described in #767.