What exactly is the purpose of having a moisture barrier outside of the studs?
Is it to prevent moisture from getting into the wooden stud wall system?
If so, they why couldn't he compensate for the potential rotting of the bottom plate on his wall by putting borate rods (Impel or Cobra rods) into his bottom plate to prevent wood rot of that bottom plate, and just let the outside surface of the wall studs get wet the occasional time that there's a hurricane in Detroit?
I know that's not what the code says, but wouldn't that protect the wall system from moisture? After all, if moisture is going to penetrate the brickwork, almost all of that moisture is going to dribble down the inside surface of the brick veneer. It's not going to jump from the brick veneer onto the insulation in anything less than a hurricane force wind, and in this case, if Gopher has extruded foam insulation between his studs, that water is gonna drip off the insulation and just get the wood studs wet for a day or two until they dry. In that case, the only concern is the bottom plate of the exterior wall which may get wet from water penetration through the brickwork.
PRG, Inc. - Impel Rods
Borate rods (either Impel or Cobra rods) are a borate compound that dissolves in water. Borate rods are preferred by owners of log homes because borates are highly soluble in water, and so borates are the ONLY wood preservative that will diffuse through the entire cross section of a log to protect it from wood rot. Telephone utilities use both Impel and Cobra rods to protect telephone poles from rotting in the ground, and it's because the borates migrate through the entire cross section of the pole. The wetter the wood, the faster the borates dissolve and diffuse. Unless the wood is wet, the borates don't dissolve and don't diffuse.
I have 6 borate rods in each of many of the wooden window frames of my apartment block. If those window frames ever get wet to the point where they might rot, the borate rods begin to dissolve and the borates diffuse throughout the wood killing mildew and mold, including the wood rot fungus.
Borate wood preservatives are much more popular in Europe. They're not common here in North America because we tend to go with either pressure treated lumber of copper and zinc naphthalene end cut preservatives here. The beauty of borates is that they they remain unaffected until the wood gets wet, and then they dissolve and disperse throughout the wood to protect it from wood rot (and other fungi). Also, borates are the only wood preservative that's environmentally friendly. They are highly toxic to fungi and molds, but mammals like people and pets can just about eat borates without getting sick. Your typical borax used for doing laundry contains borates similar to those used in Impel rods and Boracol wood preservatives, and we wash our clothes in that stuff and wear those clothes all day with no health effects whatsoever. Also, although everyone calls them "Impel" rods, the liquid equivalent goes by many different names, depending on who's selling it. It can be called Borocol, Boratreat, Bora-Care, etc. It's all the same stuff being sold under different names.
PRG, Inc. - Impel Rods
Borates, Impel Rods, Cobra Rods, for natural pest control and rot protection in Log, Timber and Wood homes
Impel Borate Rods - Log Preservatives
But, what to do depends entirely on WHY your local building code requires a moisture barrier between the brick veneer and the wood stud wall. Hopefully GBR would know if that's because of water penetration into the wall system or not. If it is, then water will drip down your wall studs, but you may need to do something to protect the bottom plate of your wall.
The borate rods (Impel rods) you might find online are huge, often 3/4 inch in diameter by 4 inches long. Those are meant for logs in log homes and telephone poles. In my window frames I have 6 millimeter diameter by 60 millimeter (1/4 inch diameter by 2 3/8 inch long) Impel rods in 5/16 inch diameter holes, and I'd suggest those would be more than adequate for the bottom plates on your exterior walls.
What I'd suggest is that you finish your wall normally, and then drill through the baseboard into the bottom plate and insert an Impel rod in each hole. The hole has to be slightly larger in diameter than the rod to allow for the swelling of the rod that occurs as the Borate rod absorbs moisture and gets to the point of dissolving in the moisture in the wood. The depth of the hole is irrelevant. But, once a borate rod starts to swell, you cannot remove it from the hole it's in. Not easily anyhow.
I'm thinking that protecting the wood in your wall from rotting may be the second best alternative to preventing it from getting wet in the first place.