What is limiting the amount of braking force applied to the rear wheels via mgu-k application of regenerative braking??? Have anyone been using shunts to bleed off extra current that the battery can't absorb? Also, what about just throwing a bunch of excess current to the mguh under braking? Once the rear tires and brakes are up to temperature, you could reduce the chance of overheating by using more mguk braking, which is liquid cooled and away from the tires
If you can't get rid of all the rear braking energy to the battery, would it not be possible to just feed it to the turbo, and or some big resistors (air or liquid cooled)