I'd love to see this feature too.....we're having a hard time with this issue in some of our departments, and there doesn't seem to be any good solution for it right now.
I'm on version 12.1 and I can see something that looks interesting in Setup > Tickets > Options > Allow Non-User CC Updates (checkbox)
The info balloon on it states:
Allow Non-User CC Updates
Indicates whether to allow Ticket updates, via email, from people who are not helpdesk users, but were CC or BCC recipients on the Ticket update e-mail.
I think this would do it for you...
You're correct, thanks! It only allows updates via email, so we still have CC'd users clicking on the web links and being denied access, but at least we can explain to them this workaround.
It's ok as a workaround, but it should be easy enough to permit CC'd users to put Notes into the tickets if they're in the CC field....hopefully coming in a future version!