If Berserker is to keep bleeding as a primary facet of the profession, tying bleed mechanics more strongly into either afflictions (boring but achievable) or damage thresholds (potentially messy) is certainly necessary, as the current progression for this route... doesn't exist. Scaling up the bleeding delivered by Bloodlet based on the number of physical afflictions seems like the best solution here, rather than reducing the requirements for Bloodflow. Why? Simple. As a Bleedzerker, I want you to clot. Shatter is based on combined health/mana threshold and Vesselburst is not a finisher: it is designed to punish people who are trying to play 'smart' by not clotting. Giving the profession a more reasonably achievable method of achieving high bleed numbers is the only way to make it a relevant part of the kit. However: I agree with those who have said that it should not be included in the profession.
The philosophy behind the inclusion of bleeding in the Berserker kit is, to all appearances, to provide a method of reducing mana for shatter. There are a few mechanics tossed in to supposedly allow a user to punish someone for trying to play around this fact and gain extra damage but, on the whole, the entire thing remains toothless (obligatory DK-related pun? maybe) due to an apparent fear of the profession having "too much synergy" with a certain other bleed-based profession inside the circle it originally belonged to. Which brings us to the real question: How can we give the profession a way to more organically reduce a target's mana, using the parts of Berserker that arleady function well, without "over- synergizing" with other bleed- or mana-based professions?
Suggestion 1: Rage. The current buff provided by high rage really isn't worth maintaining in exchange for permanent recklessness. Keep that debuff, as it encourages active spending of rage, but remove the weapon damage buff and instead allow the mana cost of Warchants to be split between the Berserker and the target based on the Berserker's current rage. For example, at 0% rage the Berserker pays the full cost of the, while at 80% rage the target would take mana damage equivalent to 80% of the chant's cost while costing the user only 20% of the normal mana.
Suggestion 2: Overwhelm. 20% bonus damage to a shout that is already on the weak side really isn't a fight-changer, which is what you're looking for if you've managed to push them to 60% health as a berserker. Change Overwhelm to instead, at 60% health, induce a timed effect (duration scaling to number of physical affs?) that causes eating herbs to incur a mana cost.
Suggestion 3: Manaleech. Idfk, maybe adding this affliction into the kit somewhere will help if your 'zerker happens to be really good at affliction tracking and I'd love to see more Fitness-related tears, I guess.
The goal of any serious change should be to develop a mechanic that is both achievable by a Berserker in a reasonable amount of time during a 1v1 fight but not immediately available for your team to repeatedly smash targets with.
Honestly, Berserker just seems unfinished. The biggest problem with the bleed portion of the offense is that Bloodflow, their only ability capable of delivering haemophilia... requires the target to already be bleeding by ~25 or more. This simply won't happen unless the person you're fighting somehow already can't clot. Adding a way to track a target's bleeding will be great but also ultimately pointless without remedying this, unless you're looking to use bleeding as a way to whittle away mana for Shatter or something equally ridiculous (and unfeasible with the current numbers).
The speed of shield attacks doesn't really seem like an issue to me. 2.9s for three affs, with an extra one tossed in by Eviscerate every 10s, is a pretty workable rate considering affs->damage is the only synergy that exists in the kit. As I see it, the things Berserker is most hungry for include a way to deliver impatience, toxins on Bloodlet, more accessible Bloodflow, and maybe some shoring up on the defensive side.
Edit: Also, make Warchant damage con-based. That will definitely help and is not silly or unbalancing.
If you really really really really really really want to use vivisect, breaking first both arms with hemotoxin/butisol followed by both legs with opium/opium might give you enough time for the 6s channel. Just be aware that a fair handful of professions can break channeled attacks even while prone/disabled with monks, all knights, and rangers/amazons being among them. Not to mention the fact that anyone can just tumble away.
The unfortunate truth is that not much is viable for Deathknight right now outside of either building bleed with a teeth enhanced longsword to capitalize on fleshburn damage or hammering away with axes. This means there really isn't a "long game" option and the class is now wholly momentum-based. There are a few fiddly gimmicks you can try with scimitars and toxins but they're unreliable. The good news is that both of these strategies are pretty viable and smart affliction stacking + bleeding will blow holes in almost anyone.