Recent clutching at pearls over the shadow docket remind me of the sensationalized stories, misunderstandings, surrounding executive orders:
No, the shadow docket isn't the Court executing a power grab. The docket doesn't involve any addition or changed powers, just as an executive order doesn't allow a president any more power than he already has.
Instead, the shadow docket is simply a different way for the Court to implement its usual authorities more efficiently, for cases where the full argument procedure is wastefully involved.