Will be interesting to see how this pans out for Snap. When I was at WeChat, I saw this idea wisely rejected. When I was at Messenger, I launched+failed to grow a similar feature (Chat Extensions). Launch partners look great!
Problems preventing it from taking off before:
1. Paucity of genuinely killer usecases
2. Lack of traffic to this part of UI (even in 1B+ user app); hard to form new habits
3. Can promote ~20 apps, but discovery not scalable for long tail, even w/ sharing
4. Dev cost > Dev return
If you're trying to make a dev ecosystem around something new, can't just tack it on as another little gimmicky feature in your keynote. You have to have specific conviction on why you have this in the app and pursue for multiple years. Will Snap be able to do that with minis?
(It is also worth pointing out that "build a sustainable dev ecosystem" isn't necessarily the success criteria for minis; it's the first thing my mind jumps to as a platform nerd, but it's possible snap is thinking about this from a different angle!)
Oh, and 5. Social discovery bottlenecked by rate of group chat participation, apps w/ actual group usecase, which differs among apps/demos. Not sure how Snap is on this.