Just started on this yesterday to test this concept. Besides labels, I have completed adding and removing of checklists.
I see its application where you need to share a cards with your external party without them seeing the other cards. You move the copy of the card to a separate board and the mirror should work because it is based on card id.
I think the challenge is to handle users changing 'names' like checklist names...to track the mirrored card's checklist id, I will probably have to add a lot more into the dictionary.
This is probably something you have in Unito
https://www.loom.com/share/e6b68fd19cd64d42ad65f809de8fa4d5
Welcome any feedback and or interest.
Working with just a copy of a card on my own board, I am able to get the 2 way sych for labels, due and due completion, all of checklist and checklist items create and updates ...done. Now I am working on Custom Field Items.
Update: CF done. New CF pending.
The setup is done when creating a copy of the card. Nothing fanciful at this point.
Indeed the are many areas to look into, but I am think of the use case of someone needing to share a card e.g. to a client on a separate board. So comments will be assume to internal and so will card members.