Plugins - Request Coalescing

[cejast]

Ability to coalesce multiple, simultaneous requests into a single one. Similar to how Varnish/nginx behaves:

https://varnish-cache.org/docs/trunk/users-guide/vcl-grace.html
http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_cache_lock

Would work particularly well with a solid caching mechanism