copy paste keyframes of multiple layers at the same time

This will probably not happen until 15+ years, if ever, so in the mean time you should download this script:

https://aescripts.com/keyframe-presets/

You can copy/paste multiple keyframes from multiple layers,.
You can save selected keyframes into presets on a list.
This list can be exported and imported as a setting file.

Brilliant!

Please add the ability to copy/paste a multi layer keyframe selection. When all properties exist on both layer - just add the keyframes, when properties don't exist, copy the effects along.

I really miss copying multiple keyframes on multiple layers.
How about when selecting keyframes would copy/paste keyframes
... and selecting layers WITHOUT keyframes would copy/paste layers. Simple content-aware copy/paste function we have already in AE.

It would be great you can simply hold down a modifier key to indicate that you want to past keyframes across multiple layers, as opposed to simply pasting layers.

*Edit: it will unintuitively duplicate your layers