But there's more to this than the policies of the app store, which could easily be changed if Apple desires. The bigger issue is iOS as the platform for the future of computing.
It is pretty well known that apps on iOS are limited to operation inside a sandbox. This sandbox limits access to the filesystem as well as various APIs and capabilities. These limits have a lot of practical benefits for mobile devices, such as increased battery life and security. However, they come with a serious cost.
There's an entire world of capability and possibility available in the operating system and services running below the application sandbox in iOS. This world is simply off limits to developers outside of Apple.
If we think of something like Siri, such a service simply could not be developed and delivered by a third party. It simply requires integration and access beyond what is capable by a sandboxed application.
If iOS is the platform for the future of computing, shouldn't it allow developers outside of Apple to help define that future? Or instead, must we wait for Apple to invent the future and maybe provide a way for developers to tap into it?
The truth is that Apple won't always be the source of the major breakthrough innovations in technology. Apple makes amazing products, but I also want to see them continue to make amazing platforms where innovation can flourish, as they've done with their past operating systems.
Tim Berners-Lee created the World Wide Web on a NeXT computer. NeXTStep was a brilliant operating system that went on to become the core of Mac OS X. Shouldn't the future of computing live up to its past? Shouldn't it be possible to build and deliver the next big advancement on the iPad Pro running iOS? This is what comes to mind when I think of a "pro" computing device and I believe this is what we will lose if iOS is the computing platform of the future.
I agree with Stephen, the future is anybody's game. And this is why I think it is so important to ensure that creativity and innovation are able to flourish outside of Apple. If iOS is destined to be the platform for the future of computing, it must take this into consideration so we do not lose the ability to participate in the creation of the future.