3
What else ? Probably everything else which isn't in a Block (Login, User Menu, Main Menu etc.) - without understanding how feasible this is ! Some things are already configurable as you point out, and pulled by the theme, Sitename, Banners also - but part of the problem, as a new user, is that you aren't aware of this or understand the system conventions. So it's sort of 'all or nothing'.
Perhaps the difficulty with this is that it would need to be Theme specific, so an admin UI would be on a per theme basis - although not obligatory and perhaps only done for one. Initially I'd probably just do an admin panel for Xswatch4 and make this the default theme. So a new Xoops user would see this first and could be directed to the Theme Admin UI, immediately change the theme interactively, and be up and running within a few minutes.