Separate the timeline and the curve editor

Yes please. Allow user to see a faint ease curve between the keyframes, and provide a bezier handle on either side of the key to re-shape the curve. (Maybe only on selected keys to keep it uncluttered)

You have all that already, just bring it together in the one UI to avoid switching.

Also I think OP's title is supposed to say "Unify" the timeline and curve editor??? They're already "separate" - that's the inefficiency, right?

An updated graph editor would be great to have. Something like Maya's graph editor would be awesome, where you're able to zoom out further than the comp's restrictions to see handles & keyframes that lie outside of the timeline.

fwiw, I use a custom shortcut to switch from keyframe view to graph view.

A separate graph editor window from the keyframe timeline would be great.
It's such a pain to constantly switch between graph and key frames.

Wow this is three years ago and still not in AE? Come on Adobe! Get to work!

and cool would be , if we could change the in and out point of the layer by moving the points around.

One of the best optimisations I'v made in AE was putting the Layer/Graph toggle hotkey on to Tab. By default its some weird keybind.

This would be really great to have. For now, there's Flow: https://aescripts.com/flow/ (but you can only work with 2 keyframes)

Undock the graph editor button from the timeline window and allow it to be a stand alone window in the workspace. Tired of clicking back and forth, back and forth...all day long