I have been using KA since elementary and missions is really my childhood memory. It's sad that it's gone, but it would still work now. Most of the snippets are in course mastery now but the "recommended" random recommendation (like course mastery) is not yet fully established. I did some research in the community help center and found that many people liked the randomness in the world of math, in which you could and will trace back to previous linked knowledge if you didn't know something. that said, it will not break the learning structure much. I know that missions are based on an old code base and are not requesting KA to rebuild it using millions of work, but maybe problems will ease just if this random suggestion feature (especially, the example of masteries of the world of math) is there. it will very much increase the playfulness that made me like KA. people just accept what they are recommended and prob stick with it.
i consider this a simple feature that won't require tons of coding, but it works wonders.
I use both Mac and ipad (ka app), and i wish this feature could be recovered on both.