Really!? That would be a pleasant surprise but I am sceptical until I see confirmation. Based on the size of the rotors, it looks like the 5 has the same front brakes/calipers as the 3 (11.8", makes sense for component sharing and cost) and rear brakes/calipers as the CX7 (11.9" bigger than the front for the potential added weight in the back).
A MS3 has 12.6" rotors, which are pretty substantial for OEM (370Z has 12.6 front), and stops about ~12 feet less than a 5 from some of the online numbers (apples to oranges comparison: more weight and master cylinders *might* be different but can prob swap that too). Assuming if the callipers are indeed the same you would only need a MS3 caliper bracket (~$40 each) to fit 12.6 rotors onto the 5. Everyone should be jumping at this to improve braking along with a nicer set of pads. The only other thing you need to make this a mini bBK is SS brake lines, which I image are available and cheap for the 3 and interchangeable on the 5. Its not +13 rotors (some require 18 rims to clear) or multi piston callipers but think how much are you getting for such a small investment.
BBKs are nice to look at but not worth the price unless you are going all out all the time or don't know how to use your money better (you wounldn't be driving a 5
). We are talking $2-3K vs a few hundred bucks for substantial improvement.
Im surprise no one has done it or try to do it.