I would wager stealth, invisibility, deception/illusion, and teleportation will all be at least minor themes. at least as far as the assassin goes. they're not really clear if the shadow power source is one of hidey-ness or evil/unaligned-ness. For example, would the shadow controller be similar to the warlock? Do infernal and star (or even... DARKNESS) pact warlocks have a place in the shadow power source?
Try to imagine how the role could be filled out. Martial had a lot of emphasis on weapons, divine on radient damage and channel divinity, primal on transformations, arcane tends to all lean towards controller regardless of role. If assassin is the shadow striker, what is the shadow defender? the shadow leader? the shadow controller?
My off-the-top guess on a shadow leader would be lifedrain effects used to benefit allies, or possibly temp hitpoints (which have a much less holy healer-y taste).