But if it's about having the font directly in the bundle encoded in base64 to save a http request, you can do that with webpack for example. But from what I understood, base64 encoded content is often slower to load than the same content served over http 2.

I don't know if others are automatically downloading the fonts to include them in the build. It's a nice feature but you can also install many Google fonts from Npm.

I guess the "innovation" here is that they also support the download step?

Either way, fonts are bulky binaries that don't gzip well but do cache well in browsers when combined with central CDNs so this seems an anti-feature for reasons other commenters point out. Most common fonts are going to be faster to paint from the cached CDN than letting it bloat your bundle sizes.