On Tuesday, at the Linux Foundation's Embedded Linux Conference in San Jose, Denys Dmytriyenko gave a fabulous talk entitled "Qt5 & Yocto - adding SDK and easy app migration from Qt4" where he talked about some work he has been doing and is hoping to present for inclusion into the OE mainline.
In essence, if you have a Qt application that you want to add to your OE build and you want it to work regardless of whether your build is adding Qt4 or Qt5 to your device, you will most definitely want to take a look at the work Denys is doing. Specifically have a look at meta-arago and the qt-provider.bbclass and qt-vars.bbclass.
He then discussed how someone would use the various SDK options to work on their Qt code in conjunction with OE. I won't repeat that information here since it's all readily available in the docs and various other places.