I'm afraid Svelte with typescript will loose some of its charm. Typescript is a little more verbose and explicit, also it cannot be directly executed by the browser (so you need to compile it, yet it is intermingled with HTML at times — there's JSX for that but Svelte kinda wants to NOT go the JSX/ShadowDOM route)

Internally Svelte uses TS though, the author claims to love TS also! It just does not mix very well with Svelte.

Stencil.js and lit-element are better picks in this regard IIRC.