4.2 is coming to the PTR soon (source) and, at least right now, Strength will only give 1 AP instead of 2.

Innervate will also now give 5% of the target's mana, instead of the caster's mana.

I've been having some issues with Rip getting severly bugged out (4k crits), so it wouldnt surprise me if rake was having some issue as well. I've posted the issue on the US bug forums, so it wouldn't hurt to post some additional info/logs.

Datamined tier 12 4-piece set bonus tooltip (wowhead link). I assume it actually extends berserk by 2 seconds.

Suppose we glyph berserk and ferocious bite. Base energy regeneration is about 12.4/second, including clearcasts and windfury (which I assume only affects clearcasts) and assuming an average offensive ability cost of 38 energy. For simplicity assume 50% crit and no miss chance. Then we have a 1/2 chance to obtain 5 combo points in 3 CP generators (4 ways to achieve this, each with 1/8 probability). The chance of requiring 5 CP generators is small (1/16), so we can say an average of 3.5 CP generators are required to generate 5 CP.

Let us also assume an average CP generator cost of 39 energy and an average finisher cost of 32 energy (realistically these will vary slightly with haste). We use 3.5 CP generators and 1 finisher per berserk extension so each extension costs 3.5*39+32 energy. Therefore if n is the number of times we've extended berserk and h is our haste value,

energy available during berserk = starting energy + (energy regen)(time) = 120 + 12.4(1+h)(20+2n)

energy spent during berserk = (berserk multiplier)(energy per extension)(number of extensions) = 1/2 (3.5*39+32) n

If we spend all available energy during berserk, this yields

n = 6.2(1+.67h)/(1-.42h)

and the berserk is extended by 2n seconds.

If we have 6% haste (i.e. not stacked at all), the berserk is extended by 13.2 seconds. If we stack 15% haste, the berserk is extended by 14.6 seconds.

Suppose we use berserk during bloodlust. The haste hard cap for bloodlust, assuming no miss chance and an average ability cost of 38 energy, is about 18%, so assume we are not haste capped (though realistically clearcast randomness will blur this cap). Then the same analysis applies. If we had 6% haste before bloodlust, we have about 38% after bloodlust and the berserk is extended by 18.5 seconds -- nearly the entire duration of the bloodlust!

Edit: at 3.5 CP generators per finisher as we've assumed, the GCD will actually limit the number of extensions to 8, for a total duration of 36 seconds. This assumes no miss chance and that all finishers are used at 5 CP.

It's conceivable that at some point GCD's become the limiting factor in extending Berserk. The absolute limit for extending it with 5CP finishers is +20 seconds. This falls to +14 seconds max if you need 4 GCD's (including misses, non-crits, etc.) per finisher. Obviously it would take pretty good gear and RNG for this to become an issue, but it's a factor that needs to be considered. For this and other reasons it may actually be better to attempt a refresh with less than 5CP, especially when Berserk is close to wearing off. This is a pretty fun bonus, and should also give the people who enjoy simming some busywork for a while.

It's always dangerous to assume, but I'd be pretty shocked if the dot does not copy Ignite's behavior. That includes the Ignite munching issue, but due to the differences in mechanics between ferals and fire mages I'd expect it to be less of a problem.

Well since we usually spam Shred (or at least use it several times in a row, interrupted occasionally by re-applying Rake/Rip/SR/Mangle) or even Mangle when attacking from the front, or as a berserking bear, I do see "munching" problems ahead.

For rogues and DKs, it is filtered a bit since it only procs from critical strikes (though, munching might exist here, too, if offhand auto-attacks proc this as well, but that's not our topic)
Hunters and warriors deal instant damage, at least for warriors even on abilities that have a 4,5/6sec CD anyway.

Out of curiosity, what 2pt finishers would you be using? Rip and Ferocious Bite both disqualify (on account of being damn horrid with 2 combo points). A two-point Savage Roar already lasts long enough to stay up the entire Berserk. Sure, you can use it 'for free' (as essentially you'll generate the energy cost in the GCD it took you to put up SR), but even so, I don't see it being worthwhile.

And while I like the idea of 20seconds more of Berserk, I still have my doubts about its actual usefulness. Berserk is only so-so when you don't actually have energy to spend during that time and even in the current length of Berserk it is easy enough to reach the bottom of your energy bar. At zero energy, those two seconds extended Berserk basically just mean one more Shred (or, the energy reduction of half a Shred).

The idea looks appealing as it promotes going into Berserk with a bit of a plan - get to 5 cp and then Berserk for a guaranteed 4 seconds (seeing how you can get a second finisher in during Berserk), but other than that I can't see it having as big an impact as people are hoping for in optimal conditions.

I'm sorry, I wanted to agree with you, but in retrospect, I just said the same things with different words

Though, I understood munching as a new crit overwriting an Ignite from a previous, larger crit, thus preventing part of the previous Ignite's damage. But you're right, we don't use Shred every GCD, or even every second GCD after the initial buildup (especially once we have Hungerer, staying low on energy will be beneficial)
I think a large factor will be the tick rate, 4 ticks every 1 sec or 2 ticks every 2 sec. The first of course would be way better.

15 seconds uptime, 1 minute cooldown. Every single ability takes us below the 80% needed to trigger Hungerer. There is no reason to be low on energy just for that trinket.

I believe you need to lose 80% of your max energy to proc it, not be lower than 80% of your max. That is to say, you must be at 19% or lower energy, not 79% or lower.

That might, usually, be easy to do, however in a situation where we'd likely be using a Berserk and getting a lot of extensions, it would likely be one where we have a lot of pooled energy and a haste buff, such as heroism, getting us a lot of bonus energy regen. In such a scenario we would be spamming abilities essentially every GCD, likely as part of a burn phase, and not dropping below 20% energy easily.

Perhaps one way to get the benefit would be to let your energy dip below 20%, Tiger's Fury, then Berserk to get the TF buff, as well as the trinket proc, for the first part of your berserk. While I believe it's usually slightly less than optimal to pop TF and 'zerk together normally, in that situation it may well be worthwhile.

You're right - completely misread that as 'whenever you lose 20%'. The one-minute internal cooldown does line up neatly with an unglyphed Tiger's Fury though.