As a GNOME user who uses the occasional KDE app under GNOME, I haven't
followed the KDE4 testing threads too closely.

However, I was wondering if there is, or is going to be, any sort of
migration of the application status config files kept under ~/.kde to
~/.kde4 ?

I thought that actually logging into a KDE session might do it, but at
least through GDM your only session choice is KDE3 at present. However,
if you start a KDE app (e.g. kate) under GNOME, you get the KDE4 version.