GNOME is not necessary anymore. It was in the past, not today. We have Qt that really works, much much better, and with LGPL license. You can run stellarium, VLC or Marble in Mac or Windows without problems. If you try to use gimp or inkscape in mac it opens x11, copy and paste does not work(in inkscape it copies pixmaps instead of vectors!!), what a botched job. In windows you will have a lot of problems too. GTK su…
OpenGL support sucks in GTK and QT equally. Especially if you want a more recent version of GL.
OpenCL does not depend on your widget toolkit in any way.
> Let GTK die and improve(or fork) Qt.
Qt is not really as great as you seem to suggest. It's a bloated "batteries included" framework that has everything from it's own string type to wrappers for things like threads and sockets. GTK is a widget library that is a lot leaner and meaner in comparison.
These massive platforms that try to wrap everything in the underlying operating systems to a common API use only the least common denominator of the systems that it runs on. The easy 80% works quite well but things tend to fail miserably when you enter the 20% realm. Things like memory mapped files or asynchronous socket i/o tend to be missing from these wrapper platforms.
And Qt is still using an old non-standard conforming version of C++ to achieve portability to things like Symbian. And their own C++ extensions that require you to use their build system and pre-processing tools. So you can't really use Qt without going all the way to Qt land.