Due to Huawei ending its bootloader unlock program, and HMD Global/Nokia never having one to begin with, Motorola is still the king of customizable budget phones (in the United States, anyway). The company just released the Android 9 Pie kernel source for the Moto G6 Play, making it easier for developers to create custom Pie-based ROMs and recoveries for the phone.
The kernel source code package is for 'Aljeter,' the codename for the Moto G6 Play. You can download the code from the source link below.
Android 9 Pie kernel sources are now available for the regular Moto G6 (codenamed "Ali") as well. You can grab them from here.