My gut feeling is that there's a nontrivial chance that the moment 3rd-party app stores are available on iOS, Meta will immediately move their apps to one to work around privacy limitations the App Store currently imposes on them.
I also strongly suspect that one of those apps would be WhatsApp, which is an app that a not-insignificant portion of the world uses to communicate. Unfortunately, I don't have a choice in what apps my family around the world uses, so I'm stuck with WhatsApp. The choice for me would either be to cut contact with dozens of family members, or enable the Meta App Store.
My hope is that if Apple is forced to allow 3rd-party app stores, they'll make it possible to even more strictly sandbox apps from those stores somehow.
I share your concerns but the immediate response I have to them is "needs more regulation."
We shouldn't let Meta take advantage of regulations towards Apple. We should use it as an opportunity to write more regulation of both of these entities for the purpose of serving the end user.
I'm not sure if this is exactly what you're asking about, but submitting an app to the App Store currently performs pretty stringent checks on things the app does — including automated scanning for usage of private system APIs and ensuring that apps include appropriate reasons for asking for access to private data (contacts, photos, location data, etc.).
Without certain forms of review, it's much easier for apps to exploit weaknesses (whether in the OS, frameworks, the user, etc.), and I can't imagine that Meta would self-regulate any more than they are forced to now. Their apps and SDKs already hoover up as much data as the system will silently allow, but I'd rather not be forced to expand my device to them, if possible.
I also strongly suspect that one of those apps would be WhatsApp, which is an app that a not-insignificant portion of the world uses to communicate. Unfortunately, I don't have a choice in what apps my family around the world uses, so I'm stuck with WhatsApp. The choice for me would either be to cut contact with dozens of family members, or enable the Meta App Store.
My hope is that if Apple is forced to allow 3rd-party app stores, they'll make it possible to even more strictly sandbox apps from those stores somehow.