After working in After Effects for a decade, I have two ideas that would streamline the animation process substantially, especially regarding the tedious process of making changes to timing. Please let me know if there are already features such as these - to my knowledge there are not.
The first concept is keyframe groups or linked keyframes.
Consider how changing the timing of a simple motion currently works.
In this example, lets say we have multiple layers, each with keyframes on multiple attributes (position, scale, transparency, and an effect attribute like brightness). These keyframes line up with their start and end points across layers, but some attributes such as brightness have one additional keyframe in the middle. Lets call all of these keyframes a group.
Now imagine that I want to extend the end point across to 5 seconds. A simple task in such a simple example, all I'd have to do is select all the end keyframes and drag them across to my playhead.
Easy done. Although I will have to move that center keyframe as well, if it doesn't rove across time.
But now imagine that this composition contains 200 layers, each with complex interractions, multiple groups of movements all overlapping with one another, even within singular layers. This becomes an absolute nightmare to retime if you have to make changes to timing.
You have to go through layer by layer and make sure you're selecting the groups properly. You'd move some layers (especially precomps that already contain animation), and leave some layers where they are moving only their keyframes, extend the timing of only select portions of the groups, and rearrange any middle keyframes according to the individual attribute's needs, all the while trying not to disturb other motion groups and not to miss any keyframes that should live in the group you're moving. Tedious at best.
My proposed solution is an option to define keyframes as being part of different groups. These groups would appear in a panel in list form and or potentially as an overlay on the timeline (like the easing view). In this seperate panel you'd have two sides.
The group list: Expandable group names which when dropped down contain the attributes and layers that certain keyframes fall within.
The timeline view: Across from that, a timeline where you see the start and end points of different groups as bars, lining up with their adjacent row in the group list.
You can grab the start, end or middle point of these bars and drag it, just like you'd do a clip on the regular timeline. This would leave the corresponding layers where they are, but move the grouped keyframes accordingly. Additionally, if you were to stretch or shrink these bars, any keyframes that fall between the start or end point which are assigned to that group will either float across time and fill the space, or stay the same distance apart in their relative position to the start and end point (if perhaps you have the option to put a group inside a group).
If you select a keyframe on the regular timeline it automatically selects the group that it lives within on the group panel. If you shift select multiple keyframes it will select multiple groups. Perhaps there is also the option to Ctrl+Shift+Select both keyframe groups AND regular timeline layers so that you can move both groups and certain layers (like the precomps mentioned earlier) at the same time.
In the group list perhaps you could have the option of going back and forth through the composition flowchart to see groups that are not within the comp you're working in, and or assign keyframes to groups even across multiple compositions. As a bonus feature, perhaps compositions could have more of a temporally hierarchical relationship between them. E.g. the master comp that contains many precomps is where each of the precomps derive their internal timing from should you select this option. Changing the timing of something in the master comp changes certain attributes of linked precomps that live within it. Perhaps you move a Pre-comp, and any keyframes that were linked to outside of it remain in place if you didn't move them in the group panel or master comp.
The best thing about this feature is that even though it could be a bit of a learning curve for many people as far as workflow goes, it removes the need to use certain expressions - boiling it down to perhaps a create group or assign keyframes to group button. And despite the learning curve, if you don't ever assign anything to a group, After Effects continues to work how it normally does.
The second concept is a simple one. Layer folders.
Certain layers sometimes cannot be pre-composed for various reasons. One example is that you have expressions applied to certain layers and precomposing will ruin those expressions, or maybe you want to keep the vector attributes of a shape layer but precomposing messes up certain effects and expressions, even when using 'continually rasterize'. Another issue is that sometimes you want an adjustment layer to effect some layers beneath it, but not all. Or maybe you want to use 'Preserve underlying transparency' but again, not for all layers below. Not only that, but the timeline gets incredibly messy on big projects. And "Mr Hidey" 
Hence - layer folders. It's pretty simple - just collapsible, renamable, maskable, effect-able, colourable folders in the layer stack that contain layers if they're sitting right next to each other.
You could have options for layers within the stack to use preserve underlying transparency on only layers within the folder, or if you put an adjustment layer inside a folder it only affects layers that are in that folder. You could even put folders inside of other folders - just like photoshop.
There you go those are my ideas. Please comment your thoughts, and - how does it work here - upvote? Subscribe? Whatever you need to do if you want these concepts to be implemented.
Thanks a tonne,
Jesse
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