I have just uploaded Qt 4.8.4 to experimental. Apart from being the newest upstream release of the 4 series, it adds the basic support for coexisting with Qt 5. Because of this support it will need to go trough the NEW queue though, so we will need to be patient.
Developers will be interested in qtchooser, the tool that allows to switch between Qt 4 and 5 development apps. It has also been uploaded to experimental.
Of course, all this has been possible thanks to the efforts of the wonderful Qt/KDE team =)
Update: our efficacious FTP masters have already made Qt pass the NEW queue. Thanks a lot!