<security hat>
Sounds like you are arguing in favor of keeping this bug. An attacker could use it to move laterally once behind whatever proxy/WAF limited the content body size.
</security hat>
Even without any proxies/WAF, PHP is always run (except in development environments with `php -S localhost:4124`) behind a web server, usually apache or nginx. Not sure about apache, but nginx defaults to a limit of 1MB for the request size (via `client_max_body_size` https://nginx.org/en/docs/http/ngx_http_core_module.html#cli...) and I can imagine apache have a similar default as well. Even if you allow requests to carry 1GB of data, this is still not exploitable, and if you have that large requests anyways, you usually find another way of doing the transfer than using plain HTTP requests.