Some good points.
Regarding Thomas' "sipping", though, (and I'll put this in spoiler tags because it save me the effort of checking to see whether any part of this violates the spoiler rules):
I think he was specifically trying to sip so lightly that none of his 'victims' would even realize that anything untoward was happening. In earlier books, however, I believe that he had been routinely feeding from Justine, though short of causing serious harm to her. My recollection was that while there was the constant temptation to "go all the way", he was able to control it yet still was able to exert himself. It was only when he was critically wounded and near death that feeding from Justine caused significant harm to her.
This would argue in favor of having a middle ground of some sort.
Distinguishing between "combat" feeding and "at leisure" feeding makes a good deal of sense. At first I was going to argue that RCVs always use combat feeding, but then I realized that the don't; they subdue their victims with their narcotic saliva, then feed from an artificially willing victim, much like a WCV.
So perhaps the system should look like a combination of some of the thoughts above:
* First, a vampire can only "sip" from a victim (enough to barely sustain the vampire, but little more) that has not been subdued. Only a victim rendered unable to resist allows the vampire to feed more deeply. Taking a target out with Incite or Addictive Saliva would certainly qualify, though more conventional means including knocking the victim unconscious also work.
* Once the victim is subdued, the target can feed from each consequence consistent with the vampire's feeding habits (emotional consequences for WCVs, trauma for RCVs). The vampire can inflict new consequences and feed from them if consequence slots are available. Either way, the vampire can benefit from one consequence per exchange spent feeding (starting with mild and working upward).
* Each consequence fed from allows the vampire to clear one
lesser hunger-related effect; feeding from a severe consequence allows a moderate or mild hunger consequence to be cleared, and feeding from a mild consequence can clear a single hunger stress box. If the vampire kills a victim through feeding, then he is sated (at least temporarily): clear
all hunger stress and hunger consequences.
Note that the above rules still allow a vampire to feed while in combat, but require a victim that has been 'taken out' and takes several exchanges to accomplish. It might also be interesting to add in a control roll to simulate the struggle Jimmy referred to. Perhaps after feeding from each consequence, the vampire should roll Discipline to control the urge to feed from the next consequence, then the next, and so on until the victim is dead.