I would like to push notifications from my plugins to the UI and have them displayed in a similar fashion to the announcements and would like to avoid adding my own notification framework if there's already something existing.
Has this already been done somewhere? I've modified the announcement plugin and would do a pull request but on the other side it feels like such a crucial feature that I'm not certain if it already exists and I might have missed it. If not... it's coming soon 
Related:
Hasn't been done yet. I wanted to add a plugin hook to it but so far haven't gotten around to do that. I'd definitely welcome a PR against maintenance that establishes a hook to extend the registered feed sources. At least one plugin has worked around the missing functionality in that regard by ninja-editing the configuration file, however that is really not a good approach as uninstalling the plugin also won't remove that again.
It has been done before...remember this dicussion...
Instead of forcing it enabled though you should just add it and allow the user to pick if it's enabled or not....
https://github.com/jneilliii/M33-Fio/blob/42296152e78c9380b184bb2884379afc9463d011/octoprint_m33fio/__init__.py#L961-L987
But you would have to setup a page to be able to load the xml file from. Like a personal github.io page possibly.