This actually came up a full three times for me this weekend with other forum members at TMC Connect. Tsportline was on people's minds given their booth at the show, and owners of their current 19" wheels seem really happy with them, but I wish there was a 20" option and so did the other members that brought it up.
The 21"s are not very well-suited for daily driving. I have a track car with higher profile tires that gives me pothole nightmares when I drive it on the street, I can't imagine going thinner still.
That said, the sizing on the 19"s seems very rare, and we can't get any of the best-in-class summer tires in the stock 19" sizing. I would LOVE a way to get factory look wheels like these in a size that allows us to retain similar-to-stock overall diameter, particularly one that supports Michelin's Pilot Super Sports.
If that existed, I'd absolutely buy it, and I think a lot of others would, too.