At the moment, when a web service provides manifest for PWA, the site should be loaded to promote or install the app.
Proposal
It might be useful allowing rel="web-app"for <a> and <area> which indicates the target link supports web-app. Then, browser vendors might be able to promote the web app before navigating into the link.
Example
<a rel="web-app" href="www.my-service-supports-pwa.com">
From what I understand, Chrome only promotes installation if the user is engaged with a website, so I don’t think Chrome would be ok with promoting installation before the user has visited the site.
Yes, that’s true. If that’s because we can detect manifest only when a site has been loaded, this might help I think.
This might be very similar with what is called “Desktop PWAs link capture”. But “Link capture” would work for already installed PWA. OTOH this new rel might help install the app.