I don't think you should expect a single massive casting. They pretty much showed the next step, which was several large modules with exterior panels bolted on (around 1h8m into the presentation, "
The Unboxed Process"). Basically assembly of large sub-assemblies (front end from dash forward, back end from rear seats back, structural pack with seats and center console, bolt together and attach body panels), they even indicated the plan for these large sub-assemblies to already have been through integrated diagnostics to be sure that internally all wiring connections are functional and so on, so that they only need to worry about connections between these assemblies after putting them together. And perhaps importantly the throwaway comment, "Just like Cybertruck."