But don't all the common devices (drones, commlink, decks, rccs, hosts) already have the ability to run personas anyway?
Hosts are not devices that can be modified, so scratch that off the list.
Drones likely do not; you cannot base your persona on a vehicle (including drones) unless it has rigger adaption and you have a control rig. The combination of the two allows a character to jump in, thus subsuming the vehicle icon by the riggers persona. At least, that's how I understand it.
Commlimks, RCCs, and decks, absolutely. If you want to form a persona on anything else, like a toaster, a smartgun system, an RFID tag, or even your own wired reflexes, then the device needs the persona modification.