What most critics miss about its hardware is that the few closed subsystems have no access to system memory and storage. It is <i>very</i> different from say a ME module into a CPU, or a closed card stuck into the same bus with the disk controller, which is the case of just every "open" laptop out there. USB, i2c and SPI are effective measures against malicious hardware taking control of the system bus and sucking data from peripherals.
Even in the unlikely (but technically possible) scenario in which some chips loaded with malicious firmware attempt to sniff the i2c bus, they will be fed data that has been already encrypted on a system memory, bus and storage they have no access to.<p>If the user encrypts the data before sending it, whether the 4G modem/WiFi/BT are closed or not, they will see just noise.