I think the perf jump from Ruby to Rust is much greater than .NET Core to Rust. Not much will change in .NET land for the foreseeable future. I see this migration happening from Ruby and others so it is not surprising from that aspect.

Also - what he is talking about was true for well over a year. It is just that a lot of day-to-day gaps between prompt and output were closed in the meantime. In a sense, Ruby on Rails/37 Signals is a late adopter.