For the past few days on the Qt development list there's been a long discussion taking place about Removing Wacom support in Qt5.
The Wacom input support for Qt5 is pretty much in a broken state but it's not the Wacom input drivers at fault, major Qt applications are troubled by broken Wacom support, not many Qt developers actually care about Wacom support, Digia has only provided a hack for Wacom support that was rejected from mainline, and there's a host of other problems.
Going with the interest level from the Qt developers, there's also very few Qt developers with actual Wacom tablet hardware. From the thread's creator, "Myself have a room with 40+ workstations where the driver is installed/uninstalled at least once a week, it's a nightmare...Thing is, it's been two years and it still doesn't work well. The bug tracker is filled with unresolved bugs, begging and ranting."
The actual Qt-Wacom problem? Ariel Molina, the thread's creator, went on to say, "I want to bring back attention that this bug affects even Qt development tools, i can reproduce it in at least 40 computers where the sole presence of the Wacom drivers makes QtC and most apps almost unusable due to the 'driver' errors and general slugginesh."
As an alternative to removing the Qt Wacom input support entirely, an option would be to conceal the Wacom tablet support behind a compile-time switch like --enable-wacom for those wanting to build-in the broken Wacom support. The support level for Wacom seems to vary by operating system with Qt where under Windows it appears to be the worst.
Marius Storm-Olsen of Qt Nokia (well, to be acquired by Digia) says, "Obviously we have a tablet laying around somewhere, under a pile of dust. I just said since this person left we haven't been working on it. Feel free to scratch the code if the itch is bugging you!"
Unlike the GNOME developers that seem to be all tablet/touch-centric these days, that's not the case in the Qt camp. From Intel's Thiago Macieira, "Sadly, our current support for tablets is very, very limited. We know it breaks every other release -- since it is never tested before a release, it breaks; then we get bug reports, it gets fixed, and then in the next release, it breaks again." Thiago went on to say that QTabletEvent (a Qt class that contains parameters to describe a Tablet event) will "never be delivered."
The only developer on the Qt development thread really pressing for the Wacom/tablet support to be improved is Boudewijn Rempt, the KDE Krita application developer. A few others have expressed interest in seeing the Wacom support improved, but beyond offering help in the form of bug reporting, no one has stepped up to the plate. If any developer cares about Qt and Wacom/tablet support, you may want to step up on this thread otherwise the support is set to be removed or at the least to be disabled.