This is more intended to log thoughts than to be a coherent essay.
I know I can use PowerPoint to do this. I did that for one of the local cablecast channels for two years. Hooking up a Raspberry Pi zero and using LibreOffice to push a repeating slideshow would not be too hard but for the problem of updating the slideshow.
I had been considering the notion of using a modified version of feh that was not from the package archives. That could be used to set up a slideshow. I hadn’t had the chance to test it yet but if I understood the mechanics correctly I could have a fixed set of filenames in a directory that feh would flip through then I could use sftp to replace those files dynamically as needed. The filenames would be something like “first”, “second”, “third”, etc.
Technically the “video bulletin board” that I referred to yesterday is more technically referred to as non-interactive in-vision teletext display. At least one GitHub repository exists with software to decode teletext that could then be piped into OBS Studio or other software and then sent downstream to a streaming service. This requires further investigation.