Regarding ESP8266WebServer:

When serving files from SPIFFS, have the option to add Cache Control Header. Having this option makes for example serving static javascript files much much better as the ESP does not have to continually serve up unchanged files.

    HTTP.sendHeader("Cache-Control"," max-age=xyz"); 

proposed implementation

  void serveStatic(const char* uri, fs::FS& fs, const char* path, uint32_t max-age);

Any thoughts for or against such an addition? I'm willing to / attempt to implement it.