on https://www.sitemaps.org/protocol.html it says:
"Also, all URLs in a Sitemap must be from a single host, such as
www.example.com or store.example.com. For further details, refer the
Sitemap file location"
(https://www.sitemaps.org/protocol.html#location)
since all urls in the list are to external hosts it does not seem as
if this would be valid.
maybe i can extend the html with structured data annotations instead
http://schema.org/SoftwareApplication. i would think search engines
can do well with html.
i will probably implement this at some point.