Rob Dolin at Microsoft and Marcos Caceres at Mozilla (et al) did a ton of work to add things like IARC rating, screenshots, and category to the Web App Manifest spec. https://github.com/w3c/manifest

You already know who owns the site, because they own the domain. You have all the information you need to ingest their app into the app store – no need to make them build a native app wrapper, submit it to the store, redirect their users to the native app, and go through all that hoopla.