Ability to "reference", rather than just import, external AE projects
It would be fantastic to be able to reference other AE projects into the current project, so that if one of the comps in the referenced project changes it will update where it is referenced as well (not unlike when working with imported .psds or using dynamic link with premiere). This would be tremendously helpful in situations where multiple artists are sharing assets (especially for character animation/character rig/background art projects), as changes would propagate where needed rather than have to be recreated anywhere else that asset is used.

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Aaron Jones commented
I need this so badly for character animation! It would be lovely if that was an option when you import it - choosing a full import or just a reference / 'link'.
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Oscar Höglund commented
Really hope this becomes a feature very soon, especially since the functionality is already in the program with dynamic link etc. For example, If I have a character rig in a separate AE-file and import it into scene comps in a master AE-file, it will import a copy and not a reference of the rig. This means that if I need to update the rig down the line, I have to manually update each scene that has the old version of the rig in it.
A reference option while importing would solve this since it would update the rig file in all comps it is referenced in and speed up the workflow tremendously!
If you don't know what I mean have a look at any 3D software, for example Maya's reference editor as a good solution. It should have the function to point to a specific comp within the referenced file. This way you can have one file with multiple rigs in it.