In most cased the inner fragment could be made into a custom View, and those work a lot better. Most new Android developer do not make enough custom views. They are the fundamental unit of UI re-use. It's relatively simple to extends FrameLayout or RelativeLayout, encapsulate a view normal views, layer your logic on top, and you have a nice usable component.

However, in our v1 the only fragments that share an activity are our main feed & story view. All other's have their own activity. It made data flow a lot easier, our manifest file a lot cleaner when filtering for intents, etc.

Interested to hear any tips if you have them!