Oh, this is cool! :clap: What license are you releasing the code under?
I'm glad you are staying similar to the libgdx (Java) runtime, but I would prefer if it were modeled exactly after it. I think it's important to keep the APIs identical, as it gives feature parity and makes it easier to document, debug, maintain, and implement new features.
You seem to be missing the BoneData, SlotData, SkeletonData, etc stuff. This is important, as it holds the setup pose information. This information can be reused for many Skeleton instances. Also the setup pose needs to be combined at runtime with the animation to allow for procedural effects.
It would all make more sense if it were documented, sorry about that. I've been in multi platform build/packaging/installer hell for 5 days now, but it looks like I'll be able to go back to working on the runtimes very soon.
The official C# runtime will need to match the libgdx, Corona, and C++ runtime APIs exactly. If you'd rather not do that, I may still be able to make use of a good deal of your work, if you are willing to release the code under the same license as the official runtimes (Simplified BSD License). :happy: