is this solution considered a hack or is something that we can use as an approved workaround in scenarios where we need to manually trigger validations?

I don't think we need more tooling here.

(Note that you're responsible for handling any race conditions that arise as a result of the component being destroyed before the promise resolves, though assigning state inside a destroyed component is harmless.)

I think we could even broadly caveat that by saying “do whatever element you want” but don't expect Svelte to care about following any HTML spec, etc.