I actually thought it was a bug that the mirror cards were not appearing on another board's timeline view. For my use case (creating a master timeline view with card content of other boards) not having this functionality makes the mirror card feature not useable. As a workaround, I'll just have to create duplicate cards which is less than ideal.

Very excited for the Mirror cards feature, and initial use with our team is positive!

However, as many Trello users work not only across different Boards, but multiple Workspaces across our enterprise license, the ability to create a personal board and mirror ALL cards/projects that a user might be associated with onto a private/personal 'User' board is something my team has been wanting for years. However, the lack of the basic calendar/timeline features for a mirrored card is a subpar Trello experience.

Being able to see the calendar/timeline (and hopefully Calendar Power-Up) features in these personal boards with mirrored cards would be a tremendous help. We would further layer the (personal/member's) Trello board calendar within Outlook for better time management insight (when is checklist A due for Card X and how does that align with all of my Teams/Outlook meetings for the day? etc.).

Please escalate the calendar features for mirrored cards! This has the potential to be a game-changer for many, but as it is now, the mirrored cards are still not quite the solution.

If this is the place to vote for the project "view mirror-Cards also in calender view" i hereby like to vote for it. Would be extremly useful! Greeting from Lutz

Similar request as other commenters. Love, love, love the addition of the mirroring feature but can't really leverage it as much as I'd like. Mainly due to the issue of the due dates not reflecting on any of the calendar power ups except the originating board.

We work on a daily news schedule - so missing the due date, in calendar view, on a mirrored card from our Video team's trello board makes it very hard for us to plan our week. 

I create a board for each of my clients, and I also create personal monthly boards to help me get a more holistic view of my capacity. Cards now mirror, but I need to be able to see their due dates on the monthly boards 

Yeah, mirrored cards are a step in the right direction, but need some work! I wanted to use them to create a master board, but the filters don't work on the mirrored cards either, so renders them a bit useless IMO.