Upstream: https://secure.phabricator.com/T4863
When projects overlaps or a project is so huge that is actually several projects, we would have cards assigned to multiple projects.
On a project work board, It would be rather nice to show the other projects a card belong to.
For example the ect-october-2014 project landing page shows open tasks that belongs to #Code-Review or Bugzilla-Migration. The associated work board https://phabricator.wikimedia.org/project/board/35/ does show the card but does not display the other projects.