For the new page "System Notifications", there is no Public API currently.
Most of the texts are served from the UI.
Surely Product Management would be happy to see idea with the reasoning behind the use case.
This would be beneficial when Dynatrace is integrated with a ticketing solution. I could see it in our case where say a OneAgent update notification is available would be able to generate a ticket interally.
In my case I would like to be notified when my environment Host Unit Quota is reached
(You've exceeded your host units quota. Your license allows you to monitor hosts with total host units up to 368. Not enough?)
So have access to API Notification content, or allow to configure System Notification to send external notifications (like mail, ...) will be good