I am using SvelteKit in "production" (smallish) for multiple projects. Aside from the small ecosystem (where in reality I am only really missing a UI lib other than IBM Carbon), Svelte has no error boundaries yet. If an error is not caught, the whole app crashes with no way to recover, or even show the user to refresh the tab. See https://github.com/sveltejs/svelte/issues/1096.

Other than that, Svelte + SvelteKit is awesome. I would not choose React or Vue for small(er) projects.