@girish I totally understand your point. My suggestion was not about Cloudron maintaining a fork (I will explain myself better).
The idea is more about reducing friction for users who want/need a custom build, instead of everyone having to run their own “loose” installation.
Since Mattermost remains AGPLv3 in the open source edition (without the limitations that their official pre-built binaries include), there could be a middle ground:
Cloudron could allow users to select a custom build in the app configuration, similar to how today you can choose between the Team and Enterprise editions.
Cloudron can simply add a disclaimer that running a custom build is at the user’s own risk, in case the app breaks or is unsupported upstream.
This way, it remains collective and consistent for all Cloudron users who need this, without putting extra maintenance burden on the Cloudron team.