How can we let people subscribe to activities in order to get email notifications whever there are updates?
Project:New_contributors/Roadmap#Notifications has some ideas about how this can be handled in the future, and Echo (Notifications) & Flow cover this use case in their roadmap. However, what can we do here and now? A simple Google form to collect email addresses in a spreadsheet? A simple web interface to collect those email addresses in a CRM?
The use case is simple:
Penny is interested in helping out in QA activities. She subscribes to receive notifications. She gets a notification whenever there is a new activity scheduled.
The Wikimedia community has tried to solve this problem o top of MediaWiki in several ways, all inefficient: relying on registered users signing up in pages, relying on people watching pages regularly or having email notifications enabled and paying attention to those notifications in the middle of the many other MediaWiki notifications they receive, missing those not willing to signup publicly, risking typos in wiki syntax, vandalism...
In the meantime, the WWW solved this problem around 1996 if not earlier: go to a web page, add your email address and be done with it. Or something along these lines.