The AppImage team provides tools for upstream packaging, so that the original authors of applications can provide binaries with end-to-end control over the all aspects of the distribution.
As a a general best practice measure for security, we discourage people from downloading software from "random places" which is everything but the original authors's download page.
@ecmu has already put in the work and has made https://github.com/ecmu/geany.AppImage/blob/master/.travis.yml. Now it is a question of whether the Geany team would accept a PR to the official repository so that the AppImages would be officially created (and supported) by the Geany team.