Something I find myself wishing for more and more is the ability to import compositions from other AE projects as components.
For example, I have a selection of end card animations that need to be adjustable for localisation, but also need to be kept consistent across multiple projects. When I make a change to the end card, that needs to be reflected in each of these projects.
I'd love to be able to have a single 'Endcards.aep' project and be able to import comps from that – then, when I place them into another composition, they would act as pre-comps with any essential properties exposed. The only difference is that they would not be openable or editable.
Later, if I make a change in 'Endcards.aep', and then re-open my other projects that refer to this, the end card comps would be automatically updated (in the way that other footage files are automatically updated).
Essentially – Mogrts inside After Effects. This would allow component libraries that are always kept up-to-date across multiple projects.