I like the idea of a standard font which is used in Scribus styles as default. If I remember right Adobe do the same thing in Indesign. They uses "Minion Pro" if I'm right.
It doesn't matter if Scribus will uses a unified font on all operation systems or one OS specific font. In any case there is a danger that people will use the standard. Whatevever.
But if there will be a standard font Scribus have to check if there is a newer version of the "standard font" already installed. In my point of view a good font shall have different font weights, a huge range of supported languages (languages specific characters) and some specials, like ligatures.
A bit off topic: Personally I would prefer to have some hand picked font set which come with Scribus. It is easier for beginners to start with some presets, similar like color sets. For sure professionals will create their own "package" of ressources with fonts, templates, etc.