The artifacts property on repo version doesn't return all repo version artifacts
The artifacts property on RepositoryVersion assumes that artifacts are all directly attached to RepositoryVersion Content:
RepositoryVersion | Content | Artifacts
But with DistributionTrees, this is not the case. There are also artifacts nested in repos:
RepositoryVersion | DistributionTree | Repository/RepositoryVersion | Content | Artifacts
This means that not all artifacts will get exported when the DistributionTree is exported.
Have the artifacts property method call a Repository method to determine what artifacts it has. This is needed since RepositoryVersion is not typed. Then pulp_rpm (and other plugins) can override this method to add in artifacts from DistributionTrees.
Add a hook to the artifact export code that will allow plugins to define what artifacts belong to a repo version.