Modernist Cuisine-style BBQ brisket safety I am going to try Nathan Myhrvold's 2-step BBQ brisket recipe: Smoke at 149F for 7 hrs, then vacuum seal and sous vide at 146F for 72 hrs. However, (due to travel for work) I won't be able to complete these steps in the consecutive days leading up to the party.

What I would like to do is smoke the brisket about 6 days ahead. After smoking, I would wait for it to cool just enough to vacuum seal, rapidly chill in an ice bath, and refrigerate until I return and start the sous vide bath. Can I be confident that a 10-12 lb brisket, after 7 hrs at 149F, will have reduced enough pathogens to be safe to refrigerate for 3 days? Or more practically, will it be safe to eat after 3 days refrigeration followed by 72 hours in a sous vide bath at 146F?
I am not aware of any rigorous tests done on a sequence like you propose.  In the absence of data, I simply assume holding any open cooked product more than a week in the refrigerator is risky, smoke notwithstanding.  

You can significantly boost your safety by soaking your brisket for at least 24 hours in an acidic salt bath -- perhaps with some brown sugar and aromatics for added flavor.  Consider, for example, a recipe like Alton Brown's corned beef, which IMHO is tasty.  (Add a dry rub of fresh-ground black pepper and, say, a little fresh-ground allspice and juniper, and you have pastrami.)

By the way, after smoking you don't have to wait for your brisket to cool: any vacuum bag suitable for immersion/sous-vide cooking can easily handle a brisket right off a 150*F smoker, no cooling/waiting needed.  Besides, if you submerge the still-hot brisket after sealing in its bag into a 150-160*F water bath for 10 minutes, you will have effectively Pasteurized your product; with the residual salt and acid, I personally would be comfortable holding the sealed bag in the refrigerator up to two weeks (if I needed longer I would freeze it).