Kubuntu is not a separate distribution, it's the Ubuntu packages and compile options, just with a different default desktop.
I would be very disappointed if the kubuntu folks decided to throw away the Ubuntu resources (repositories, testing, bug reporting, etc) that are spent on all the diverse packages available just because they use KDE instead of Unity as the desktop.
One of the really good things about Kubuntu is that it doesn't force people into a choice between Kubuntu and Ubuntu, all desktops are available, and can be installed at the same time with it being a login option which one to use. If it becomes a separate distribution, a log of this is lost