I think there is a niche this would fit into. But I think it needs to be three things

1. optional
2. securely fashioned
3. high quality

I’m picturing a normal flat back phone that that this attaches to with strong magnets, would appeal to people who want a better camera but not quite spend the money on a dlsr. And if its optional then I’d be able to finally sit my phone flat on the table with or without a fat case again.