Defold uses its own "runtime" implementation.
Or to be more correct; during the build step we build/compile spine-scenes into our own format. This means we can add support for other animation formats in the future and don't have to depend on Spine specifically. In turn this also enable us to render spine animation with our internal batched rendering.
Sadly, there is currently there no way to follow specific issues. We track them internally at King, but they are not available publicly at the moment... We are working on a public roadmap though!
From what I can see, the issue DEF-1217 is planned for 1.2.85, but this might change so I can't promise anything.