I'm glad I found this thread. I also apologize for resurrecting it after a lengthy quiet period. My team is currently working on an official Spriter runtime for Torque 2D. We just had a review of the source we have generated so far, and the topic of blending came up. With the acknowledgement that blending in Spriter itself is planned, or at least desired, we are hesitant to add our own implementation.
We came to the same conclusion that to support blending in our runtime, we would be dependent on the Spriter animation to share all the same bones and references. While this would work, I believe it will be flimsy. Not knowing how the format of the data might change, our implementation might have to be tossed completely to support what the Spriter team comes up with.
Any way, I just wanted to jump in and say we (the T2D user/developers) would love to have blending. We will not take a leap of faith on our implementation until it's officially supported in Spriter. We are going to structure the Spriter animations in Torque 2D in such a way that it will be possible to support blending in the future, but we'll have to follow the topic closely as Spriter matures to see if changes need to be made on the fly.