I seem to have missed this, but Smart Lists can now be shared across work spaces.
To be more precise: Folders containing Smart Lists can now be shared and the Smart Lists inside that shared folder are now visible for Smart Campaigns that live in other work spaces. A huge improvement!
Yep, this was enabled about a year ago. But better yet, in January, you can actually reference those shared smart lists in your smart campaigns across workspaces. This is a huge time-saver for us (since we have 23 workspaces).