I would be over the moon if this "mapping" could be done with the same curves we now use for interpolation between regular keys.
There's a Mac interface prototyping tool called "Principle" that does similar things, but the way the "states" are linked is not the best. It's just not apparent what the source and target are there.
And sorry to be mean, but the best animation interfaces I know are Maya and After Effects, but you guys come a close third! 😉
-In all seriousness, Spine is good at getting out of the way. I regularly find myself in "the zone" using it - thank you! 🙂