I understand and agree with the move to Mastery. I'm a fan of spiral learning. Spaced repetition, too, I've enjoyed Supermemo and Anki for a long time. I've been slowly adding Supermemo into my daughter's learning process, but having that outside of the Khan universe leads to a demotivating experience for her as it's obviously not gamified. I'm glad we can phase that out.
I don't agree with fully removing missions, however. Does it mean we will no longer have views like this:
What missions gives me is an easy and unified view into my kid's status in World of Math, pre-algebra skills, etc., and to each section of a unit. This level of granularity in a single place is great! I can direct her to practice an area more if she needs it. She can jump around between units and even grades. While that's not ideal, it keeps her interested and putting the time in. If she is struggling in an area, I can see that at a glance and give her help. She doesn't like help. Although she's slowly getting over that, because it's a work in progress, I still like to be strategic about how I offer help. Seeing the topics she is "struggling" in helps me do this. I snip the mission skills page each day and paste it into OneNote, so I have a history of her struggles. This allows me to tailor other projects we do outside of Khan to give her additional work on her weaknesses in a real-world context. I need what this tool provides, it's how I compete for her attention with the three X's: Roblox, xBox and Netflix.
I realize it is still possible to get all this data through progress or by logging into her account, but the experience is cumbersome and time-consuming in comparison. Maybe I'm missing something else.