Is there a GUI for the feed reader newsbeuter?
Or would there be an easy way to create one for it?
Or is there any other graphical feed reader that could use the
cache.db database (SQLite) of newsbeuter?
No, there is no GUI for newsbeuter. It does, however, have an export option to print subscriptions to either
stdout or a file; see
Export feeds as OPML to stdout
You could simply export your subscription list as
.opml and import the list into a graphical client of your choosing.
unor, if it's been some time since you looked at Liferea, maybe take another look. I'm using version 1.18.12 on Fedora with about 400 feeds with no real issues. I found earlier releases to be buggy and very slow to update. Update speed still doesn't match something like NetNewsWire on OS X, but it's tolerably quick.