Digia announced that Qt 5.4 Release Candidate is already available for downloading:
According to the information from their team meetings this release candidate should be very close to release version which is expected later in December.
This version contains large number of bug fixes, also versions of MinGW and Mac OS used were updated. Now Yosemite is used for packaging.
List of new features in version 5.4 can be found here:
The most interesting thing, to my opinion, is that in this version they consider Qt WebKit module done. Though it will be supported in future, later they will be developing Qt WebEngine. It is a new module appeared just now and based on Chromium.
They are not going to support Qt WebEngine on all platforms, only some of them. You can read about that here:
Many new features for WinRT and Windows Phone platforms were added in version 5.4.