I've seen reports of this, that the response in the Rivian forums was overwhelmingly negative. For people bringing comparisons with Tesla, Tesla had a long history of cancelling base versions of cars, so by now most people expect it. In the start, Tesla also used software locked cars to deal with base orders (remember the 40 kWh Model S?)
Rivian however is dealing with all new customers with no previous history, so most people will feel a sense of betrayal. I can see people that can still afford it, cancel just on principle. This can kill the impression of a lot of potential customers at a critical juncture in their company's life.
It seems Rivian has walked back their position after huge negative response (as well as from the stock market):