Recently (Release notes July 2024) we’ve been given the ability to set up and edit the details of custom fields (Asana Help).
Also asana is rolling out Team Sharing for projects.
I think it would be awesome to marry the two and be able to add Teams with certain specific access rights to the custom fields.
A logical next step, indeed! 
Agreed.
Adding my support for this feature.
I really like the idea of having a TEAM Custom Field library, where those CF’s can be shared across the projects within the team, without having to share them across the entire organization - the only current option for multi-project CF use.
Rough example of what I’m imagining, utilizing the same privacy UI from the project creation process:
