I'm not sure. That's partly why I need to borrow that VAG-COM. VAG-COM will tell me as much about the car as VW's own diagnostic tools, which is a lot more information than generic OBD tools report. At the moment my OBD tool isn't reporting any codes.

The cat is after the turbo, so any oil in the cat must have been through the turbo. However, when the engine is cold, or when you are cruising off-boost, the turbo won't burn the oil. In fact, the oil would need to sit in the turbo for a while before burning - the turbo itself is oil-cooled. I did originally have some concern that maybe the turbo was letting go, but it still pulls as strong as it ever did. The normal failure mode for a turbo is that its bearings self destruct at 120 000RPM, and the turbine/compressor wheel ploughs into the housing as a result and destroys itself in the process. Generally loud, noisy and irreversible. Perhaps overfilling the oil created excess pressure and caused the oil seals in the turbo to blow by, and that could be a problem - oil seal blowby is often a precursor to failure. However, the amount of oil that came through the engine originally was huge. Huge-blue-turn-the-clearest-day-into-foggy-night type smoke. And now, despite the code-less misfiring, I don't see or smell any evidence of oil from the exhaust. It is also normal to have some oil in the intake tract anyway. The crankcase ventilates into the intake tract in order to burn off oil fumes. (By design, an emissions thing,) So I wouldn't expect an occassional drop of oil here or there to cause this problem.
Coilpack failure... could be caused by excessive overloading of the coil according to anecdotal evidence. I think that 900 miles of fighting oil in the combustion chamber would probably qualify, although impossible to prove. The same evidence suggests that partial failure is a possibility. If the problem is only in one cylinder (which I suspect it is) then the coilpack has to be favorite - and at $21 each, a cheap remedy.

Burnt and blocked cat? I wouldn't have thought that this could cause an intermittent problem like this. The dealership wasn't concerned about the cat when I originally took it back in after the trip, and pointed out that the post cat O2 sensor is very sensitive to cat failure. I also know that OBD would store a pemanent code and the CEL would stay on if the cat had failed, which has not happened. Remember that the CEL is predominantly an emissions light - it only flashes or lights when there is an emissions-related problem.

The most annoying thing about all of this is that it's intermittent. The car is still covered under a 10yr/100K drivetrain warranty, and will be for another 20K. But if I take it in to the dealership, and their VAG tool shows no codes and the problem doesn't show in their test drive, they're going to turn around and charge me $75 just for the priviledge. That's why I want to know if any non-OBD codes are stored. That's also why if it appears to be a single coilpack I'd be tempted to replace it myself.