While I like the look of larger wheels, I'm of the mind that we need to get back to more reasonable sizes. Even race cars have more sidewall on them, and they're dealing with much better asphalt.
For cars like the 6, which are essentially grand touring cars, they could really use quite a bit more rubber. I have the 19" M-Sport. With the RFTs it was completely unbearable. With non-RFTs (I went with Michelin A/S 3+ for all-season duty), it's night and day better. But had this been a few generations earlier, it would have had 16", 17" or at max 18", and I bet it would have been amazing riding.
Take an e38 7-series as reference, and 16" or 17" was normal, with M-Sport giving you 18" wheels. It looked just fine - fantastic, in fact. But we kept creeping bigger and bigger, and now smaller wheels look "odd" to our eyes, now trained on larger wheels. But we've given up quite a lot in terms of comfort and ride quality in the process. Meanwhile, here in the US at least, our roads in major metro areas are only getting worse, so this trend makes even LESS sense.