Rule of thumb is why the hell should any app, unless it's a web browser need a data connection unless it needs to acquire something for it to work.
I agree with unoace. The popularity of something will eventually be it's downfall. If it's security you want don't go mainstream.

As for Sailfish, can't say at such an early stage. But Jolla's watchword has been "Security by isolation". Probably meaning the Android layer isn't embedded and can be removed if the end user wishes, maybe it's built into one of the "Other Halfs".