They ought to just turn Prepared into an ability of its own as a mini-Adrenaline Rush for DH and have it replace Vengeful Retreat, if they feel so inclined. Might be a little weird to have the ability still called a Retreat if they were going to remove the retreating portion as a drawback/solution to animation cancelling for the talent. But that's a minor detail. Far more concerned with having the talents both function and not require clever use of game mechanics.
And all the same for Fel Rush. Perhaps if they halved the distance you traveled while using Momentum, you trade off mobility (without sacrificing it completely like you would with animation cancelling) for damage while having it feel a bit less intrusive to your positioning. Hell that would be pretty beneficial for targets with smaller hitboxes as well.
Well, just random thoughts anyway. I'm not so lucky to have hands on with Demon Hunter, what do I know. :V