if we make it compatible with the skeletal mesh, ue4 users don't have to implement some complex system that handles all the features related with skeletal meshes like physical animations, Rig control, sequencer animation, etc. I think this is really necessary feature on the plugin.
It is pretty tangible work though, because spine data already have all the things that need on unreal's skeletal data. general bone structure and render data are already compatible with unreal's format.
(I saw that the official plugin feed its rendering data at the procedural mesh component and use it as a rendering component, and basically, skeletal mesh rendering data in skeletalmeshcomponent also use same data on its rendering process, so it will be quite easy to change UProceduralMeshComponent to USkinnedMeshComponent (USkeletalMeshComponent))
and the features that are in spine skeletal data that unreal doesn't support on the skeleton level, (such as IK constraints, Path constraints, etc) can be implemented simply by running spine skeletal animation component's functionality inside the skeletalmeshcomponent.