Spine Support has been added to the Little Polygon SDL2 Asset Toolchain as part of the MiniLD51 "Tool Jam"
Only bone animations are currently supported, but other features are stubbed in, and will be implemented as need arises (we're currently using these tools in production for DIGHARD: C R I S I S). Even so, our implementation is a lot simpler than the generic C runtime as (i) we do a lot of preprocessing in Python to put animations in a native-friendly form, and (ii) the runtime uses a "structure of arrays" rather than an object-oriented style which has less indirection and better cache coherency. (Our terminology are a little different since we were replacing an older JSFL solution).
Python Import: http://github.com/maxattack/little-polygon/blob/master/tools/rig.py
Python Export: http://github.com/maxattack/little-polygon/blob/master/tools/export_asset_bin.py
LMK if you're interested in our tools and would like to see any other spine features exported