However Qt Virtual Keyboard was a value-add component for Qt Enterprise customers, until things changed recently.
As part of the recent licensing change announcement, Qt Virtual Keyboard is now available also with GPLv3 license for Open Source users in addition to commercial Qt licensees.
This move allowed me to finally integrate Qt Virtual Keyboard with Hawaii, which soon will also be available on SDDM.
Qt Virtual Keyboard will be included with Qt 5.7 but it's possible to build the sources from the git repository now, against Qt 5.6.
The virtual keyboard is an input method so activating it is as easy as setting an environment variable, as outlined in the deployment guide:
To make it easier and less error prone a setting for Hawaii has been added that you can enable from the keyboard settings.
On desktop systems the keyboard is resized so that it won't cover search and password text fields.
Obligatory screenshots below: