SomptingGuy
Are you referring to the 4,0l V8 TFSI Engine? From what I understand this doesn't have 'bank deactivation' per se but individual cylinder deacivation, missing every other cylinder in the firing order and deactivating both inlet & exhaust valves on those cylinders. So 2 cylinders are deactivated per bank.
In terms of analysis and testing VAG are well renowned for going to great lengths to validate and sign off their products & I would not suspect Start-Stop to be any different.
As far as the OP is concerned I would imagine that, within the EMS strategy, there would be an inhibit condition for 'Stop' (not key off) which looks at modelled exhaust component temps as well as others (coolant being an obvious one). Another major factor could possibly be the amount of O2 stored within the catalysts after Component Protection Fuelling at full load or Fuel Cut, whilst decelerating. I would suspect that the EMS would want the cats to be in a nice stable condition before switching the engine off. Particularly since OEMS have to provide for Durability Compliance with emissions testing & OBD on aged catalysts. Stopping gas flow (by switching off the engine) whilst the catalysts have a lot of exothermic reaction occuring does very little for durability!
In terms of turbocharger longevity my understanding was that the main cause of damage, to a normally operating turbocharger, upon engine stop was the local boiling of the oil within the sleeve & thrust bearings? With the fact that water cooled turbos are now pretty much a given, most if not all OEMs provision some sort of run on coolant pump - if they need it. The failure would most likely be oil egress from the cassette and this would somewhat degrade the catalysts, something that would be unwelcome due to the in use/aged component testing mentioned above.
MS