Right now we send cache-control: no-cache in response to requests for the webpack generated css and js bundles, and probably other static assets. Since these files only change as often as the Kibana version, and we already send the build number as a query param in the request to bust the cache, we should totally allow the browser to cache them. But Kibana is a single page app you say, it's only the initial page load that's slow so it's not that important. But that's not always the case.