Almost certainly bootstrpbase and clean wont switch to bootstrap 3, but there is work going on to bring a bootstrap3 'base' theme into core, although I haven't been around much the last few weeks to see the progress (if any) being made on that.
I believe the logic is that Bootstrapbase and clean will stay fairly much as they are to avoid the issues of child/cloned themes breaking if they were upgraded to BS3.
Also 100% agree with Mary's comments above. The usual recommendation is NOT to edit the core themes themselves as your edits can be lost on any upgrade. Whether to clone or create a child depends on your views on maintaining your changes and how many changes you want to make. For relatively small changes such as the fonts you are tlaking about, I'd go with a fairly minimal child theme, personally - as Mary suggests.