By viruses I don't only mean them in the classical sense, but also apps that steal your data, apps that mislead you, apps riddled with ads everywhere. That's the future if you want app stores with no oversight, and you will have app stores with no oversight if you put 0$ as the budget for managing the stores.
Today iOS doesn't allow running apps that were not vetted by Apple. And yet you can find loads of apps that steal your data, with ads everywhere. All approved by Apple.
In contrast, Android has multiple app stores that exclusively host open-source, non-spyware and ad-free ads.
That doesn't mean there will be an ecosystem of ethical FOSS app developers though. That will take much time to develop and it only being available in the EU will limit its growth. And you'll probably still have to invest in a Mac to compile for iOS.
I think the excellent FOSS apps ecosystem will remain exclusive to android even after Apple is forced to open up.