We the Debian Qt/KDE Team want to early-announce [maintainer warning] our decision to remove Qt4 from Jessie+1. This warning is mostly targeted at upstreams.
Qt4 has been deprecated since Qt5's first release on December 19th 2012, that means almost two years ago!
So far we had bugfixes-only releases, but upstream has announced that they will end this support on august 2015. This already means we will have to do a special effort from that point on for Jessie in case RC bugs appears, so having it in Jessie+1 is simply a non-go.
Some of us where involved in various Qt4 to Qt5 migrations  and we know for sure that porting stuff from Qt4 to Qt5 is much much easier and less painful than it was from Qt3 to Qt4.
We also understand that there is still a lot of software still using Qt4. In order to easy the transition time we have provided Wheezy backports for Qt5.
Don't forget to take a look at the C++ API change page  whenever you start porting your application.
[maintainer warning] **Remember the freeze** and do not upload packages ported to Qt5 to unstable. The best thing you can do now is to ask your upstream if the code can be compiled against Qt5 and, why not, try it yourself.
Our first priority now is to release Jessie, and this is why this is an early announce.