the mount could either work as an individual target that the opponent can kill first to drop the dk off, or the mount could be a "part" of the dk, improving his survivability like an absorption shield that, once reaching its limit, drops him to the ground, only being able to regain his mount while out of combat (in this case the amount of absorption would be the same for all mounts, numbers would have to be balanced of course).
the second idea is about death grip.. it is only logical that when you are pulling something towards you very fast, EVERYTHING in its path should be pushed aside cuz helooo laws of physics! when the dk death grips something, anyone near the DG target on its way back should be either knocked back or stunned, either that or simply everyone around the dk gets 1 of this when his target arrives. That would be a cool improvement to dks utility and would make the game a bit more realistic. This logic could be applied to priest's leap of faith as well.