My immediate response to this is that if this is possible, then how do we stop MaliciousPaymentSkimmerApp from social engineering people into becoming the default in-app payment provider for every app on their phone?

I mean, sure, I would like the option to replace the default camera app too, but now I'm asking myself how we make sure MaliciousCloneOfCoolCameraApp isn't sending every photo it takes to a remote server that scans for anything its owners think might be able to make it money?

(There is some prior art for this in iOS' custom keyboard world, I suppose. I was excited for those but that quickly faded when every damn custom keyboard demanded Internet access, which is not a thing I want my keyboard to have, whatever their excuse may have been.)