This is not factual because there is no law requiring or mandating tire shops not installing tires with lower speed rating than manufacturer's top speed. It has always been strongly recommended and not required. You did not consult AI on this one as you always do with your posts.
But I agree...
No need to wait. Some R1s from the Rivian Shop already have XPEL Stealth PPFed as an option. The sooner it's done (if you're going to do it), the less chance of paint getting chips.
Sure, there'll be more tires available in 21s, but they'll also be more expensive than the 20s. The 20" rims look much nicer and tires are much cheaper.
It's not like the 21s having much less sidewall than the 20s with much less comfort. It's 60 vs 55 profile. The tire noise I felt were more from the AT tread.
I do like the look of the 20s more so I chose them on my order a week ago. But a few days ago I took the 20s out for a one hour long on road and on highway test drive (my third one) and I do indeed felt more tire squirm and more road noise than I remembered as in my second test drive just before...
Well, I backed up my R1T into a light post in the middle of a parking lot two years ago and the total cost for the insurance pay out was $21K - $16K to fix the truck and $5K for the light post. That was the Forest Green R1T in my signature.