Think about it. Aside from ganking, when is Blood Frenzy used the most? In blood scion form. So why not just throw it onto the Perfect Scion Morph? Without the health drain, of course. Since now you'll only be able to make use of it when in the ultimate.
Then they could fit an entire new spell in the kit that would help round out the play style. I propose they throw in a bat-magic skill in Blood Frenzy's place.
Here is an idea for that skill:
The base ability would have to be a magicka ability. It'd be a basic gap closer that just launches you forward in a swarm of bats dealing magicka damage to every person in an AoE that you hit. This ability would have a charge up and can be interrupted via hard CC (which is the balance factor.) If it is interrupted this way it gets placed on a cool down and it allows for counter play. If uninterrupted and charged for a while, this ability can launch the player pretty far! It'd be a fun skill.
The morphs would be changed into health and magicka respectively.
The magicka morph, after you reappear, could turn you invisible for 6 seconds. Because that’s the exact amount of time it takes for unnatural movement to kick in. Say you got into a fight you don’t want to have. Simply rush past in a cloud of bats, then quickly sprint away, turning invisible and ending the fight. This skill would give people a way to enter unnatural movement in combat easier and give vampire an option for some pretty sneaky plays.
The second morph is a health ability. For each enemy you damage, you heal for a flat amount of HP that increases based upon how many consecutive hits you can make on the same target(s). So if you swarm through a lot of enemies, you will make your hp back plus more that you spent casting it. If you swarm back through the same group of enemies, you heal even more. Counter play to this would be staying spread out and not grouped up. I also really like the idea of the skill working sorta like a 'predator strike' in way, similar to what we saw in the first greymoor trailer, except a cloud of bats.
This way not only would vamps get access to a UNIQUE gap closer unlike any other in the game, but they'd have more bat-magic synergy + a way to do good AoE damage.
CREDIT for the blood frenzy onto scion idea goes to
@TX12001rwb17_ESO. I really like this idea and think it'd make a lot of people happy. Especially those that like Blood Frenzy and those that want vamp's other skills to be useful.