It would be nice if links on resource objects could give a "hint" about what HTTP methods are allowed for certain target URLs. This could suggest to a consumer of the API that the resource object is editable, for example. Concretely, this could help a Drupal admin UI "know" if it should render an edit or delete button.
In the JSON:API Comment module, this was achieved via a custom link relation type and/or separate links for separate operations. However, this expired IETF draft, HTTP Link Hints, proposes a set of new target attributes for link serializations that would achieve the same thing. It does that by adding the concept of an allow target attribute on links which hint at the expected Allow header that would be the result of an OPTIONS request to the target URL. Note that this is not supported by the JSON:API specification.
Adding new links and/or link relation types would be something that requires no specifications to be published and could be done today. It is also very explicit. The drawback is that it makes JSON:API links objects more verbose.
The target attribute approach would risk being a "Drupalism" until the aforementioned IETF draft is published (however, it does not seem active). It would be relatively concise.