I wonder if it would be possible to make Unstoppable still work in this build if it you played Cornac instead of Shalore and used the Corruption/Oppression tree. You could quickly stack up Horrifying Blows stacks with unarmed attacks, then use Mass Hysteria to spread stacks to nearby enemies and use Fearfeast to gain 56% of a turn for each enemy in range. Basically, you rely on gaining turns to get more mileage from Unstoppable instead of extending its duration. You could use Quicken Spells and Metaflow to shorten/reset the cooldown of the Oppression talents.
The obvious flaw is fighting single targets or small groups of enemies, where Fearfeast will not be able to give a net increase in turns. Hope Wanes can be used in this situation to paralyze dangerous targets for multiple turns while you burn them down with spike damage. Metaflow should allow you to do this a couple times in a row, after which you can retreat and wait for cooldowns if necessary. Extended fights that don't allow retreating (like the final bosses) might be a problem, but we'll see.
I think I'll try it out on Insane and see if the concept works as intended. If so, a Madness run will be in order.
EDIT: First run died at level 17 on Insane. The issue is lack of defensive skills before unlocking Unstoppable, but the same issue was present in the original build. It might take a few tries to get over the hump, but I suspect things will be easier after that.
Well I would say, in theory as a back of the envelope math thing, that if you can double the amount of attacks in some way or increase damage significantly or a combo of both then you can get away with less Unstoppable.
My worst case was the last fight, which was I think 15 1000 energy "normal" turns. Without using potion of invulnerability which can give you some more turns. At 210% gspeed (a good amount of this was from shalore boost though) and 180% combat speed. You would probably need a further 100% gspeed or combat speed and then use the potion of invulnerability to make up the last like 4 turns. Since it already has high speed you would need a good bit of absolute speed to see something that would say make it a 10 "turn" fight. Basically 400% gspeed would be a 7 turn fight or something (going from 2 hits per turn to 4 hits per turn would be double damage).
So if you can solve that problem in some way it can probably work. But losing shalore will lose you a lot of gspeed something like 35%.
I think if you can get the last fight down to a theoretical 10 "turns" you are probably fine almsot everywhere else with one unstoppable and can save the potion of invuln for a few extra turns of fighting.
Edit: Yeah the start is not easy, you really need to be picky and get top end equipment from drowning. The start in the Tanking build I posted is a good bit easier. The winner I posted here got a very good shielding rune (about 300 shield) from drowning and this was really useful. If you can get the Rune of Reflection from a store during the drowning it can help a lot. Basically until Unstoppable matures I did a double shield and kill fast approach or flee approach. So basically need really good gloves to kill fast and enough shields to stay a few rounds. This is one of the reasons I farted around a few zones like hidden compound trying to get an extra level or two to transition to Unstoppable. There is a rough patch around lvl 22-24 or so where even Time shield + rune starts to not match well against things HP growth in certain places.