You need to call an engineer; their job is to invent odd things (like if you ask them to create for you "a phone that rings without sound", they bring you a vibrating alert system). Why on earth would anybody want to get such a thing? First of all, most of the apps that have GUI, work really in the console. So such thing is stupid, if you can run it from the console in the first place. This is also very easy in X, running a graphical terminal app (but you didn't want to).
Why would they want to use graphical passwd replacement? Replacing a password is a matter of giving the old one and new one twice (these days, at least), and because it still is text format, then why use graphics for it? Passwd is simply, ultimately the best tool you could use. I't simple. It's small (eats up only few text lines, not a new window). It's fast. It's everything you're dreamt of..
If they want such an app, why don't they go Windows?
and if it has to be graphical and in Linux and in KDE (or Gnome), then why the heck can't it use Qt (or GTK)? Really?
I'd say your customers are odd people
as they say, good inventions shouldn't be made better..it often leads to something worse.