I would tend to second your request of displaying all Terminus fonts in setconsolefont though, as they provide a lot more sizes and codepages.
Until and including 14.0, setconsolefont displays only console fonts included in the 'kbd' source package (in ./data/consolefonts), so that would mean adding those included when installing the 'terminus-font' package. That would need that the 'terminus-font' package be installed, or (probably a simpler solution) merged with 'kbd.
It would seem consistent then to add all these terminus fonts in the initrd, as 'setconsolefont' is first (possibly) run during installation.
EDIT. Stupid me: forget previous sentence, fonts are gathered from the freshly installed system.
On the other hand that would add no less than 248 files to an already long list, so maybe it'd be wiser to let things stay as they are, unless/until setconsolefont be restructured, for instance providing a menu with several levels (for instance allowing to choose first the size or codepage, then displaying all fitting fonts). But that'd be for Slackware 14.2 or 15.0, I guess
Till then, as you pointed out, it's not that difficult to edit 'rc.font'.
In the same vein, I always find list of time zones displayed by 'timeconfig' way too long, so IMO that one would deserve to be restructured as well. But, I digress...
EDIT2 I apologize to readers: previous EDIT was misplaced