It will be interesting to see how this plays out. It makes no sense to make up a rule that applies only to Apple.
If they are going to force one company to invest in researching and developing a platform, building services and a market, setting up checks and balances, and then re-engineering it to allow people to circumvent all that makes it both secure and profitable, then they’ll need to apply the same rules to all companies large and small.
The ruling would essentially allow anyone to install anything on other people's cars, TV’s, Xbox's, PlayStations, Nintendos, tractors… everything... and not just as a result of a user's actions. Think about auto-updates. After all, we're ultimately just talking about computers and their platforms/systems. Such a ruling to allow side-loading has implications across all hardware in all industries. Even in healthcare. Another example. Say a hospital doesn't want to pay the service fees for their MRI, and a competitor provides a cheaper interface, updates, and calibration. Obviously, GE will be required to provide an interface that allows side loading their competitors' features.
Such a ruling would demand that engineers invest time and resources to create systems to support loading of 3rd party apps and services, which circumvent, replace, and alter all sorts of user experiences and services. It's not even a stretch. It's just a platform. For example, farmers have been fighting John Deere for years now, and with such a ruling, they could be forced to build ways to open up their systems and allow farmers to alter, replace, and diagnose better. Does everyone win with such open systems? Maybe. Maybe not. Another would be gaming consoles. They'd better brace themselves for it. Gaming consoles would become nothing more than lightweight computers (they are, but) they also would be required to engineer the systems to facilitate circumventing/side-loading past the business models. Has anyone consulted with Nintendo, Sony, or Xbox teams about the impact it will have on their companies and platforms?
In short, we're talking about legislating how platforms and hardware should be developed, forcing some overhead to develop those systems to allow competitors to circumvent or change their behavior, sandboxed or not, it's legislation of engineering more open systems in all industries. Interesting idea indeed.