Nate's in the middle of updating AnimationState for all runtimes and he's almost done with that part.
He thought the functionality was a good idea so he added it to the list of new features, along with reinstating AttachmentTimeline's old track-override-friendly and mix-friendly behavior.
Likely a different API than the one I stuck in there— possibly going to be a TrackEntry setting instead of a bool on the AnimationState. I'm not sure if he's decided on what to go with yet.
Either way, it's a significant change (you can see some of them already in AnimationState.java) so we'll have to wait til we finish porting.