Apple has in fact been forced by regulation to allow alternative app stores on iOS devices (at least in the EU), which matches the substance of Sacks’s prediction.

In January 2024, Apple announced changes to iOS and the App Store in the European Union to comply with the EU’s Digital Markets Act (DMA). These changes, delivered in iOS 17.4 starting March 2024, explicitly include new options for distributing iOS apps from alternative app marketplaces and APIs for creating such marketplaces.(macrumors.com) MacRumors’ coverage confirms that iPhone and iPad users in the EU can download and install apps outside the App Store through alternative app marketplaces.(macrumors.com)

Apple’s own and independent reporting emphasize that these options are limited to the EU and require both an EU-region Apple ID and physical presence in the EU, with access restricted or removed when users travel outside the bloc.(macrumors.com) Nonetheless, this still means that iOS devices now support alternative app stores under regulatory pressure, which is exactly the mechanism (“forced by regulation”) Sacks described. Subsequent reporting on the Epic Games Store operating as an iOS third‑party marketplace under the DMA regime further demonstrates that alternative app stores are now a practical reality on iOS in the EU.(theverge.com)

While the change is geographically constrained and tightly controlled by Apple, the core claim—that Apple would eventually be forced to allow sideloading or alternative app stores on iOS devices due to regulation or market pressure—has come true. Therefore the prediction is right.