John Layt of KDE has been trying to work out the printing support improvements to focus on over the coming release cycles. There's long been plans to have a new QtPrint module for replacing the QtPrintSupport module, but this proposed module would involve quite a lot of work and be a very large task at hand.
John's plan for improving Qt printing support is to write the new printing code over a few releases as a new set of QPA classes while using the current public API of the existing plug-in code. After some releases, a new API for the new code will be conceived.
With the Qt 5.3 release the hope is to have a new QPA print device API and to implement support for the three core platforms, use the new classes in QPrinterInfo and QPrintEngine, remove platform-specific code from QPrinter, replace all platform-specific code with widgets and dialogs, and improve the auto test framework.
John also has work-items on his mind for the Qt 5.4 and 5.5 releases when it comes to printing. The new printing API could possibly come in Qt 5.5. Those interested in Qt print support can find out more details on his hopeful work via this Qt development list post.