You can set bezier functions as timing functions for CSS keyframe animations but I can't see it ever being used without a Apple Motion-like keyframe editor. Since it is WebKit only functionality, maybe Web Inspector should offer it.
But how would you save the results?
Currently, we have only one option to export textual data - via the clipboard. E.g., for CSS stylesheet resources we now keep track of change history, and any file revision data can be exported by drag-and-dropping the respective tree element into any text editor that supports pasting/dropping of text/plain data. At least, we can build the CSS text and present it to the user.
<rdar://problem/15801500>
*** Bug 176484 has been marked as a duplicate of this bug. ***