Heikkinen Jani of Digia sent out a reminder this morning that the 5.4 feature freeze is effective beginning 8 August. The Qt 5.4 code will be branched from Qt's "dev" branch on 11 August.
For those curious about the new features for Qt 5.4, they are conveniently listed by the Qt Project Wiki. Among the Qt 5.4 changes are improved support for OpenGL ES 3.0/3.1, QImage now supports 10-bit per color channel images, QQuickRenderControl is now public to allow efficient rendering of Qt Quick 2 scenes into FBOs, Qt Bluetooth now supports BlueZ 5 and Bluetooth Low-Energy, the QtWebEngine component is a new module of a web rendering engine based on Chromium, QtWebKit supports an OpenGL-accelerated 2D canvas, QtWebChannel to provide better integration between web technologies and browser engines, and various other developer changes.
The official Qt 5.4 tool-kit release is expected late in 2014.