Downloading the file locally won’t do any good because you’re only pulling a snapshot of the feed data. It has no way to update live.
One option might be something like Tickr Feed Reader. This displays the feed in a customizable window on your desktop, then you can bring that window into your OBS scene. If Tickr isn’t to your liking, google “rss feed ticker” for other similar applications.
I’ve never done something like this before, but I’d be interested to hear if it works.
Only thing I'm seeing is Tickr which looks old and I'm not sure if it has dependencies on regular Ubuntu or will run on Xubuntu.
If you want a mild challenge, there are Perl or Python RSS libraries that should make it easy to parse RSS, and I bet it would be fairly easy to open a text window with a big font to scroll in.
There are close ones, but no cigar. Created your own, if you need one.
https://github.com/nicolas-raoul/Feedindicator
tickr you can run on top of your panel. You can even open up to the width of your panel. It looks like a panel extension that way.