Splitting this from bug 35306, Echo should support user subscriptions to feeds. "Feeds" in this context refers to updates (messages) from organizations or individuals that would typically be sent out as a newsletter currently. An example would be a user wanting to subscribe to updates from https://en.wikipedia.org/wiki/Wikipedia:Wikipedia_Signpost or https://outreach.wikimedia.org/wiki/GLAM/Newsletter.
Currently these updates are served to individual user talk pages using a wiki bot (cf. https://meta.wikimedia.org/wiki/Global_message_delivery), with the target (subscription) list being managed on a wiki page (e.g., https://meta.wikimedia.org/wiki/Global_message_delivery/Targets/Signpost).
Ideally a user would be able to subscribe in an easy way to a range of feeds and then receive notifications via Echo.