Seems that design limitation in TypeScript mentioned in documentation is fixed
What problem does this feature solve?
Quotation from this documentation page : "Because of a design limitation in TypeScript, you have to be careful when using function values for validator and default prop options ..." . In this sentence "design limitation" links to this GitHub ticket which is mentioned as fixed 19 days ago in this ticket.
What does the proposed API look like?
Considering mentioned TypeScript limitation does not exist any more Vue could be improved.
Assuming we don't have to adjust our types and this just works, this limitation still exist for TS <4.7 (and that version is still in beta afaik).
When 4.7 is released and we have tested this, we could move this to the docs repo and amend the docs accordingly.
Related docs PR: https://github.com/vuejs/docs/pull/1853