First off, Props for a good write up of the situation and from the same server.
Pretty much everything you have said is true (I dont have a sub 2 min kill, but I have 6 - 7K DPSer behind me for patch).
My suggestion for a high threat opener on a patch like fight would be this:
IT (as boss is running to you) 1500 ave
HoW (as boss runs in) Threat from RP gained
Thats should add up to close to 15K threat in 4 GCD of the boss getting to you plus whatever you get from RS hits plus MD and ToT.
To me its not the initial threat that is the problem. Its the sustained threat. I normally play unholy so I have alot of "down" time (not burning a GCD on something) and I would argue a unholy tank has more reason to be spell hit capped than a frost tank. The 2 main problems I have are parried/missed attacks which push my rotation off a GCD and whenever I have to use/setup a defensive CD (BS for me, UA for you) which require runes which then interferes with our threat rotation. Correct me if im wrong but I believe we are the only tank in the game that has defensive CDs that both eat a resource and a GCD. I would be fine if BS/UA took a GCD to do as long as they didnt burn a rune. I would then only push my rotation off by a GCD which I can live with as opposed to now my whole rotation is off as I wait for the rune to come off CD.
Overall though, I do feel threat on the tanks is much better than it was in TBC. And maybe we have been spoiled by the whole premise of not having to worry about threat due to the large leads, but as a DK, we are capping out the top end DPSer where as other tanks are not having this much trouble. Now, the fact that you are in Alpha (top guild on server to those who arent aware), I would assume that your DPS are burning there threat dump CDs and havent forgotten them .
As far as the picking up of adds is concerned, as unholy I think I have a big advantage here (my disease tick for a good ammount) so I can just do a double pest to catch a group that is running in. I think the change to pest has made this a much smoother issue and I actually havent had any trouble picking up add packs. But there are situations where I do wish I had an AoE taunt, but in a controlled situation, I have yet to need it.
Last tid bit, for Sarth 3D, you can burn pest without an add on you. the only problem doing this is you may get an add on you. I have yet to try this out, but someone had suggested using BB (since you can still disease him through the immunity, or atleast he gets the debuff) as that would not aggro a blaze on you.
I cast the spells that make the people fall over.