There should be a general repository for VMs that can be restored from a Backup file.
The backup file should not be unencrypted and have SHA256 hash and each backup file should correspond to a script that can generate it so it can be built, backed up, and the hash independently created and verified so the community is more likely to see attacks if they do not happen in isolation. The purpose of having a backup to easily import the qube, which could be subject to a man in the middle attack (and the SHA256 posting could be subject to the attack too) is be able to demo the VM to see if it’s worth building. Having the script is easier than complex instructions posted over several posts.
Unman has done this already somewhat with the Qubes tool but we have so many great community projects and they are posted in a way in which it takes so much time to create them for non-experts and unman’s tool doesn’t include them all.
This idea presents many risks and may not be compatible with the Qubes philosophy.
https://www.osboxes.org/ has something similar for VirtualBox, but that is not entirely open source with add ons and lacks features of Qubes.