I’ve created a Tidbyt App which you can use to show notifications from HA.
The idea is:
HA uses the rest_command to post to a MongoDB cluster (M0-Free) in Atlas (atlas.mongodb.com)
The Tidbyt app (MongoDB Notify) will pull that notification from the MongoDB cluster and display it.
It’s open-ended in that you should be able to display almost (Marquee isn’t going to work) anything you like. You just have to “draw” it in JSON instead of using the Tidbyt widgets. I have a simple notification and a placard notification in the README.md to get you started.
Just a note: It stopped working this morning. I found the “bug” (I think something was changed on the back end because it was now seeing ints as floats and complaining). Anyway, because of that, you won’t see the backend error and you won’t see your messages. I put the fix up but am waiting for them to approve it.