Qt SDK support
There are a couple of apps (example) that are written with the Qt SDK and which could be included if the buildserver would support the Qt SDK.
The SDK can be compiled from source, or it can be downloaded and then extracted.
See this as an example link: http://download.qt.io/official_releases/qt/5.7/5.7.0/qt-opensource-linux-x64-android-5.7.0.run.mirrorlist
F-Droid has this source-only policy, but the Qt SDK is pretty big and probably takes a long time to build, so what about doing an exception for it, like there is an exception for Android SDK/NDK?