It's a goal not a promise. Rivian is right in the middle of ramping production and moving this feature forward in response to demand. It could go faster or slower than they anticipated, but they are trying to give you some idea of the timeline. You can't place an order before it's available, just like all the other trim options that aren't available yet.
I received my invitation to order the R2 approximately three days ago. When I went in to configure and order I selected coastal cloud interior. The website indicated that the selection was not available and was placed on a waiting list. No surprise and happy to wait.
I received my invitation to order a few days ago. When I went on their website to configure and order, I selected coastal cloud interior. This immediately led to a prompt that informed me that I was placed on a waiting list.