It would be super valueable to let our users see only some boards based on our user type custom field.

This is something that my company would very much like to have. Currently there is a major risk of someone accidentally making changes to another board that they aren't "supposed" to be managing. If each admin role only had access to specific boards, that would eliminate that worry altogether.

Yes. Even if read-only, it would be great for the roles to be a bit more flexible