This can't be done easily because the web runtime won't smoothly interoperate with native code.
Technically it should be possible to put the animation in a WKWebView, have it emit its layout on every frame over the web view boundary, and assign layout to a native label using CoreAnimation. But at that point you should probably just use CoreAnimation.
We're working on a solution that will offer deeper native support for e.g. native element animations like you're describing here — but it's not available yet. Stay tuned!