On the Ubuntu developers' mailing list it was brought up this week about what Qt5 tool-kit will be used by Ubuntu 14.04. Right now Qt 5.0 is shipped but there's unbuilt Qt 5.1 packages in the proposed archive and there's also daily packages available of Qt 5.2. Qt 5.3 is also coming but will not make the cut for this Ubuntu Long-Term Support release in April.
Steve Langasek of Canonical has commented, "I expect we will be taking 5.2 for trusty, but currently this is held up due
to concerns about the qreal ABI change on armhf and its possible impact on apps in the app store. I'm in the process of analyzing the ABI changes for impact, and hope to be able to share the results this week. We will need to take a decision soon about how to handle the upgrade to 5.2; I'm hoping that the results of the ABI investigation will make this decision an easy one."
Qt 5.2 came last month and brought full support for Android and iOS mobile platforms, Qt Quick improvements, improved Wayland support, Bluetooth Linux support, the Qt Creator 3.0 development environment, and a wealth of other changes over its ~six month development cycle.