I'm convinced that if iOS was opened up to third party app stores, a potentially popular store wouldn't be a Facebook/Google monopoly store that exists solely for user tracking, but rather something boutique and niche like F-Droid (except maybe without the FOSS focus). The current App Store is huge and unwieldy, its search and discovery UX dated. There's ample room for third party app stores that specialize in high-quality design, or high-functionality minimalism, or privacy and security. They might even have higher standards than the official App Store.