I didn't know this, I was just trying out the project because it seemed interesting. If they can get the bundle sizes down it looks like it could be a great developer experience.
As of the latest preview of Blazor, the boilerplate template (Release build) app loads a total 4.92mb, of which ~4.5mb is the runtime. It's not ideal, but if they can manage to get that to below 3mb it's "good enough" for my purposes. As an Angular developer, at work our app bundles are no smaller than 3mb these days.