I don't think what you describe is possible.
And here is why:
1. You would need a custom mesh which adjusts to the characters body settings...If you don't do that, each character who is a bit taller or has wider shoulders depending on the body mod you use and the NPCs body settings would have his shoulders or arms or other body parts clip with the cloak. The game would have to do that on the fly.
2. As soon as you move you would also need a compatible collision object which works with the body physics so that your arms stay under the cloak when you move. Else your arms would clip through the cloak as soon as you move. (I highly doubt that skyrims physics engine can correctly calculate that...the result would be a piece of cloth which shivers and flaps uncontrollably)
3. What you also would need for the cloak is not just physics but also morphing capabilities, so that there is a "bump" in the cloak when you lift your hand a bit.
Something similar as in 1. might be doable using Bodyslide....however not on the fly...You would have to manually adjust the cloak to the body settings outside the game.
2. Might be doable under considerable scripting and engine stress to the game
3. Is absolutely undoable within skyrims capabilities (thats the kind of animation the guys at Pixar and Weta workshop get paid for.....you got no imagination how difficult it is to animate an arm under a cloak)
All in all I can say that I'm certain that something similar as you describe might be doable.....but not without considerable clipping issues. I'm fairly certain that what is doable would be similarly unsatisfying to you, for different reasons, but unsatisfying nonetheless.
Bottom line is its either doable in an unsatisfying way or undoable within the capabilities of skyrims engine.
Edited by metaforce, 27 September 2016 - 01:10 PM.