Google has now officially added a key mapping file in the AOSP Google Issue Tracker that should allow support for wireless controllers from Sony's PlayStation 4 in Android 9 Pie. In effect, that means that support for the controller - which connects via Bluetooth - will be implemented in Android 9 Pie at a system level instead of being determined by individual OEMs. As a result, users will be able to play Android mobile games with support for those types of peripherals or navigate other interfaces such as controlling movie playback with a DualShock 4 controller.
Full support for controllers in the Android ecosystem isn't necessarily anything new but is ordinarily severely dependant on whether or not a manufacturer has specifically incorporated key mappings. Beyond that, their use has been limited to game emulators that include those. However, Google has been working to build out the Android gaming market over the past several months. News surrounding that includes rumors that the search giant is working on a hardware platform of its own. That's hardly surprising since the components found in a modern mobile flagship should be more than capable of playing some fairly intensive titles but are predominantly held back by touchscreen or tilt-based controls. Those suffer the caveats of causing a player's view to be obscured by fingers getting in the way of the screen or are just not accurate enough. The addition of controller support at the system level should help eliminate those problems and allow further growth.
Meanwhile, the news of added Playstation DualShock 4 controller support actually follows earlier reports about the addition of support for Microsoft's Xbox One S wireless controller at the system level. So users with either console will now be able to use both devices to play games or navigate aspects of the UI without having to buy a specific handset or tablet. The only current console devices still not supported in an official capacity are the Nintendo Switch's Joy-Cons or Pro-series wireless controllers. There's no reason why Google wouldn't add support for those as well, beyond their current limited use in emulators but that could depend on whether or not Nintendo gives them the go-ahead. Having said that, those controllers can already be used alongside the Steam game platform for PC so it isn't out of the question.