Moreover, it was made by one of the folks who brought TypeScript support to Svelte (https://github.com/halfnelson/svelte2tsx), so although it may not be explicitly pushed by the core team, it was still made by a significant core contributor.

I'll note that React is the only web renderer that gives official blessing to a native framework, and that's because it's also the only web renderer that built one themselves rather than leaving it to the community.