Those motion tweens were added 9 years ago, so not desperately new!
If you could copy a keyframe, where would you paste it? If it's anywhere within the same layer you could select the keyframe and option-drag it to somewhere else.
Another thing worth noting is that you can select a range of frames, and do a Copy Motion, and Paste Motion that onto something else. It would transfer all of the keyframes in one go.
You could also duplicate a layer and then swap the symbol for another one.
Sorry, Colin, but you evaded my question, which was: "How do I map a shortcut to Copy Properties"
Copying a motion is only viable for the complete tween-span. It will not work on a selection of frames. See Screenshot attached. If I am missing something obvious, feel free to correct me.
The ability to copy whole motions is certainly great, but when animating you need to build up those motions before moving them to other objects.
No matter what animation software you use, the ability to reproduce the values of a keyframe, or property keyframe to use animate lingo is essential.
Sure, that works with Alt+Drag, it will create a duplicate of the selected frame or frame span and insert it at the drop point, but it requires you to do one insertion at a time, constantly re-selecting the span or frame and dragging it through the timeline, which I am sure you know from personal experience, always bears the risk of dropping it on the incorrect layer. That is not sustainable in a production environment.
I am therefore asking for a way to put a shortcut on that Copy Properties command, so I can grab a frame or selection of frames in a motion and paste it on the timeline at another point. After Effects does it, Toon Boom does it, Spine does it, even Flash/Animate does it with Classic Tweening. Because it is useful.
If there is no way to do it, no blame on you. All I want is to find out whether someone has done it. And if possible, how to achieve it myself. You did not tell me that, I am afraid.