Hi all,
The ability to copy/cut/paste keyframes across multiple layers has now been released with version 24.4 of After Effects. You can also now Paste Reversed Keyframes, including across multiple layers. For more details, please see https://helpx.adobe.com/after-effects/using/whats-new/2024-4.html#multi-layer-keyframe-copy-paste.
Thank you all again for your feedback and comments!
- John, After Effects Engineering Team