"World of Math" mission was a wonderful way in to Sal's original inspired approach and I am among those who miss it terribly.
Speaking as a huge KA fan, Course Mastery and Mastery Challenges, while very useful, do not really offer what the World of Math mission did.
While I understand why it was deprecated in modernizing the code base and focussing on standards alignment, perhaps it would be worth further discussing what was great about the World of Math mission and how its special qualities might be recreated now?
Below, I've linked to a couple of posts about it, and a search for it on the KA wikia, which will pull up, among other things, a snapshot of the old page.
Anyone interested in working on this? Might we have a conversation with engineering staff about what would be required and whether a volunteer group could be formed to help build it?
Selected Reference posts: