Qt holds particular significance to Nokia developers; it is the environment used to create applications for MeeGo and Symbian devices. More generally Qt is a well known, well liked and widely used cross platform application and UI framework. A Qt port to Windows Phone would increase the addressable developer base and result in ports of applications from other platforms.
The 'under review' label does not mean that Microsoft have decided to take action on the topic, but rather that a topic is being studied 'to help with planning ideas and to better understand how developers are using the WP development platform'.
Nonetheless it does raise the prospect that Qt support for Windows Phone might be being considered by Microsoft. From a purely technical point of view there's nothing stopping a port of Qt to Windows Phone. However, traditionally, Microsoft has been vary of 'foreign' development environment on its platforms. This is especially true for Windows Phone's developer environments (XNA and Silverlight), which almost exclusively use managed code (and tightly control the few exceptions).
When Microsoft and Nokia first announced their partnership I was told that a port of Qt to Windows Phone was not going to happen. For now, I judge that it is likely that this remains the case. Even so the possibility of Qt on Windows Phone can not be ruled out altogether. If it were to happen, it is very likely that it would arrive only with the next generation of the platform, the new architecture (kernel) of which will require a rewrite for native code portions of any application (i.e Qt would need to be ported once for the current version, and again for the next version).
In either case developers can make their views know via the dedicated WP Feedback page.