Ah, yes. But you seem to be saying in the article that these incentives cause the platforms to lack such features, whereas what I mean is that e.g. Android's intents and activities provide just such a mechanism (which could be used to great effect as indicated in the sibling comment about OpenIntents), but commercial application vendors don't want to use it. They would rather control the user experience than integrate seamlessly into the platform.
In particular, you mention sandboxes imprisoning the code. But Android allows an app in one sandbox to display an activity (essentially a dialog box) from another app running in another sandbox with different privileges in a way that appears seamless to the user. I could have one app with access to bluetooth (but no camera) call upon another app with access to the camera (but no bluetooth) in order to take a photo.
I believe apps can also expose services and data sources (ContentProviders) – e.g. your Images, Tables and Conversations – to other apps and define their own permissions[1] for them.
In particular, you mention sandboxes imprisoning the code. But Android allows an app in one sandbox to display an activity (essentially a dialog box) from another app running in another sandbox with different privileges in a way that appears seamless to the user. I could have one app with access to bluetooth (but no camera) call upon another app with access to the camera (but no bluetooth) in order to take a photo.
I believe apps can also expose services and data sources (ContentProviders) – e.g. your Images, Tables and Conversations – to other apps and define their own permissions[1] for them.
[1] https://developer.android.com/guide/topics/permissions/overv...