Define a way for websites to link to AppImage downloads

Use case:
https://kde.org/applications/ shows download links for the Windows, Android... app store.
How should AppImages be represented there, and where should the information come from?

The AppStream spec allows specifying URLs to e..g, the application homepage, bugtracker, etc. - but not to, e.g., "the latest AppImage for the stable channel".

Turns out that the AppStream spec allows for custom tags:
https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-custom

KDE is already making use of custom tags:
https://community.kde.org/Guidelines_and_HOWTOs/AppStream#KDE_customs_tags
cc
So the question is, do we need/want custom tags for AppImage downloads.

Requirements:
* The information in the AppStream metainfo file must not hardcode version numbers
* The information in the AppStream metainfo file should allow for multiple channels (e.g., release, nightly, alpha, beta,..)

Question:
* Do we want a "deeplink" that results in the AppImage being downloaded, or do we want a link to the download page on which the AppImage can be downloaded by the user?

Food for thought:
* Do we even need AppStream for this purpose? We could re-use AppImage update information for this purpose. This might completely remove the need for using AppStream to get this kind of information, it is already there and it already supports different channels

@jriddell: AppImage update information is a text string that is embedded within the first few KB of AppImages that support automatic updating (hopefully all of the KDE ones do!). From this string, the URL to the AppImage download can be constructed. Would that be an approach that would be acceptable for this use case, or do you think the information must come from AppStream?