Hi @Stephen-Patterson, thanks for this feedback!
It is currently possible to set up Rules using the People custom field: Introducing People Custom Field! 👥 - #63.
You can create a Rule similar to Trigger: People field changed > User A added, Trigger: User A added as Collaborator.
It’s not possible to add all users tagged by the People field as collaborators just yet but this is on our Product team’s radar. I’ll let you know if this changes!