One thing that has changed in around that time (maybe) is that GKIs[1] are now standard across (Google-branded) Android devices. Board/SoC support is handled via kernel modules now. The builds are directly from the Android Common Kernel, and an explicit goal is to be able to upgrade kernels on-device. (This has actually been demonstrated on Pixel devices, though I'm not sure how widespread it's been across others.) The Common Kernel also doesn't take contributions, and specifically encourages vendors to just upstream their drivers instead. Not that this fully solves the problems you're describing, but Android as a platform has become more intentional about dealing with kernel fragmentation and making itself more structurally friendly toward mainlining.
For the Pixel specifically, Google actually is working to upstream its hardware drivers and enable devices to boot off mainline. [2]
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One thing that has changed in around that time (maybe) is that GKIs[1] are now standard across (Google-branded) Android devices. Board/SoC support is handled via kernel modules now. The builds are directly from the Android Common Kernel, and an explicit goal is to be able to upgrade kernels on-device. (This has actually been demonstrated on Pixel devices, though I'm not sure how widespread it's been across others.) The Common Kernel also doesn't take contributions, and specifically encourages vendors to just upstream their drivers instead. Not that this fully solves the problems you're describing, but Android as a platform has become more intentional about dealing with kernel fragmentation and making itself more structurally friendly toward mainlining.
For the Pixel specifically, Google actually is working to upstream its hardware drivers and enable devices to boot off mainline. [2]
[1] https://source.android.com/docs/core/architecture/kernel/gen...
[2] https://lpc.events/event/17/contributions/1445/