This is odd. At first I seemed to remember Alembic having some support for Bones. But maybe I was wrong.
Alembic will not attempt to store a
representation of the network of
computations (rigs, basically) which
are required to produce the final,
animated vertex positions and animated
transforms.
So really this should not even be an option. Correct?
What is interesting is that when you import as Skelletal it creates a series of morph targets. Similar to how Blender imports the .mdd geo cache format.
And it plays the animation.
It also Plays in the sequencer. Whereas geo cache does not.
What is the reason behind this?