The only valid argument against HTTP GET with a body is that it has privacy/security risks.
Exist stuff (caches, CDN, etc.) could serve private information because the HTTP GET is cached without checking the request contents. The new standard can avoid this because old stuff does not know about HTTP QUERY.
Exist stuff (caches, CDN, etc.) could serve private information because the HTTP GET is cached without checking the request contents. The new standard can avoid this because old stuff does not know about HTTP QUERY.