Yeah, I've been trying to figure out which file is which rofl.
They have FloatingChatFrame and ChatFrame and ChatConfigFrame
All I managed to figure out to get nUI to work was to change nUI_ChatFrame.lua to reflect the new buttonframe buttons.
The chat system in general has been reworked considerably with watchframe like collapsible chatframes.
Frames I managed to locate were as follows:
ChatFrame5
ChatFrame5Tab
ChatFrame5Background > I couldn't see this with FrameStack but it isn't nil
ChatFrame5ButtonFrame
ChatFrame5ButtonFrameBottomButton
ChatFrame5ButtonFrameDownButton
ChatFrame5ButtonFrameUpButton
ChatFrame5ButtonFrameMinimizeButton