They have showed actual prototypes of multiple different aspects. Usually you start rocket design with a engine, and build the rocket on top. The engine in test

They have showed actual prototypes of multiple different aspects. Usually you start rocket design with a engine, and build the rocket on top. The engine in testing already and they seem to have nailed down the basic specs and all the important parts. That's more then brainstorming, thats actually prototype testing of specific sub-components.