Actually, AppImage just uses a userspace mounted file system for each app so it could include Qt and Python in the image if we build both of them against a base system and run very much like Apple and Windows. With no outside support needed as long as it works with the real system glibc and kernel.
The AppImageAppKit exists on github and it is a very simple c program that should build on any system. So we could pick the oldest system (Ubuntu 18) and use it to build the AppKit tools and give it a test run.
Here is the link to AppImageKit:
https://github.com/AppImage/AppImageKit
On the ReadMe near the end there is a link to precompiled appimagetools that were already built on CentOS 6 and Ubuntu 14.4. So we should just beable to use those binaries to create a test package.
You can also get linuxdeployqt as an AppImage and use it to build a AppImage using Travis CI and trusty without having to keep an old ubuntu 14.4 build system VM around.
More here:
https://github.com/probonopd/linuxdeployqt