Why not offer an option of no wheels at all? You select what you really want, have it shipped to Tesla and they mount it. Of course it would be PIA for Tesla (charge for it) and a nightmare for figuring which wheels/ties would work but it could be an option for those interested. Think about all those wheels/tires that sit unused. I swapped wheels/tires on my Z, kept old set (just in case) and ended up giving them away after a couple of years. After they took up all that space in Garage.The thin side wall is most certainly a consideration for ride quality but dampers can be used to absorb energy not buffered by the side walls. For me, the biggest difference in a change in wheels was dropping 10 lbs per corner in wheel weight. Sprung to unsprung weight ratios on suspensions has everything to do with wheel response time and the tire's ability to stay attached to the road. It also dramatically affects ride quality.
Unlike others who concentrate on wraps and such, my very first work will be on quantifying rim weight for the stock 21s versus affordable (TSW) and stupid expensive (forged/machined) 20" rims. If the current 21s are similar to previous Tesla rims there is likely a very nice ride and performance (less mass to spin accelerating or braking) benefit to be had changing rims.