Not sure how Fuchsia is supposed to solve this. If you can port those Qualcomm SoC drivers to the fixed Fuchsia interface, you could just as easily port them to the mainline Linux kernel and submit them upstream.

"Easily"? Some things can only be shipped as binary blobs. For example, you won't get open source audio drivers that support patent-encumbered codecs like Dolby Atmos.

Windows has a stable binary ABI which means that my drivers don't go stale when Microsoft pushes out a minor rev to the NT kernel. Windows does its updates and my peripherals [mostly] work just fine.