Yes, too many challenges
Thank you for all your responses. I think we have a solution now.
We started working with a continuous flow (Kanban) in order to provide greater flexibility for role-fillers to prioritize their own work.
We have a policy that all product development work is placed in the Product Backlog and is prioritized by a Product Owner role.
Let's say Bob fills two roles: a Feature Developer and a Social Media one. We added an accountability to the Feature Developer that tells that this role must consume items from the Product Backlog. On the other hand, the Social Media stores his projects elsewhere (Asana, Glassfrog, Trello, etc). This can also be standardized via policy.
When Bob wants to work, he has the flexibility to choose whether is most helpful to work as a Feature Developer or Social Media, since the Sprint timebox does not exist anymore (Kanban now). Before this policy, role-fillers would prioritize Product work in order to meet the Sprint Goal.
Summarizing, we still have two work repos. Product Development work is prioritized by the Product Owner, and the rest is prioritized by the role-fillers in alignment with the Lead Link strategy.