I've never done either one of those, but it seems to me the two-stage cooking process would be very uncertain. The second stage is not like resuming a cook starting from the end point, because you'll be starting with a partially-cooked, cold brisket that needs to be brought back to the previous end temp, during which time it will be cooking. Also, I don't know what changes in texture, etc., might occur during the cooling and refrigeration step.
It does sound like a great experiment, though. I wonder if restaurant chefs have figured out a way to accomplish this?
In my limited experience, slowly reheated brisket is pretty darn good. I've heard of reheating in hot water in a zip or vacuum seal bag, but haven't tried it. Good luck! (And report back!)