How small can you go?

As an experiment Katie was used along with patched tinyxlib and tinyxserver and the end result was basicly only Busybox, TinyX11 and Katie in ~30MB ISO image that boots into a single QtWebKit browser window. The biggest file was the WebKit library which was ~20MB, the X11 fonts were ~30MB.

Another experiment - Katie itself can be ~15MB installed (on Linux at least) if it is build with size optimization in mind such as -0s -flto -fno-exceptions along with CMAKE_UNITY_BUILD set to OFF (otherwise link time optimizations are neglected) and you do not install files such as the headers, development tools (designer, qdbusviewer, etc., qdbus may be needed as runtime dependency) and some components (DesignerComponents, the Designer component may be needed as runtime dependency).

How does this compare to Qt4/Qt5? I have no idea, feel free to experiment with the project and let me know if you do.