One option is to create a new namespace or expand the existing one. However, an alternative approach could be to leverage the RSS namespace extension for podcasting, which already includes the necessary tags. For instance, the value tag can be used to define the payment method and recipient, while the new medium tag allows for easy differentiation of content types, such as "blogpost", "newsletter", "video", or "music", as specified values. This approach streamlines the implementation process, utilizing existing infrastructure and established standards.
I use it for PeerTube RSS feeds in the Lightening plugin. it's not a perfect fit but works. The main issue I see with using it for SN is that its current implementation is keysend payment focussed with the type 'node', SN Lightening addresses were lnurl only last I checked , so you might need to extend it a bit by using a different type. Still better to work within an existing framework rather than starting from scratch.