From what?
The VAG version of the 6sp longitudinal FWD ZF slushbox was I believe only found in AWD models, so it is actually a ZF 6HP19A, and it is a very different transmission than the 5HP19FL units in the B5 Passat. It would be a massive undertaking, with very little if any payoff. The BHW has as much torque as some V8s. It doesn't really need any more gears. At 80 it is square in the meaty part of the engine's output.... halfway between peak torque and peak horsepower. Delivers good fuel economy, never needs to downshift, etc.