Allow duplicating cards, preferably via a keyboard shortcut or through the right click context menu.
This accompanied by the Copy/move to another board could be used for templates (have a board or a tag for template cards, duplicate and move them to another card).
I was thinking about this one and wondered what the primary usecase would be.
I can see two immediate cases 1) use one card as a template for others and 2) use one as the basis for others, whereby content will be updated (similar to a new version of same card). In either case it could be useful to have some form of link to the original in order to understand the heritage of any given duplicate card.
For most cards there will be no heritage other than creation date, but perhaps in this duplication use case a subtle ‘duplicate’ indicator on card could indicate heritage and permit user to optionally bring the immediate ‘parent’ to the fore so that comparison of content can be made, or so that the source template used can quickly be re-accessed.