> But it is my understanding that this is already the reality on mobile devices - most of them are based on a private kernel tree with a whole bunch of closed source drivers added.
On mobile devices, the proprietary drivers are in user space. The kernel can be recompiled (because providers are forced to provide the source for their modified kernel), with necessary patches, which helps create alternative ROMs. This probably won't be a possibility anymore with a kernel for which you don't need to provide the source code. The drivers will probably be back in the kernel and you won't be able to patch the kernel to make it work on unsupported, newer / alternative user space.
On mobile devices, the proprietary drivers are in user space. The kernel can be recompiled (because providers are forced to provide the source for their modified kernel), with necessary patches, which helps create alternative ROMs. This probably won't be a possibility anymore with a kernel for which you don't need to provide the source code. The drivers will probably be back in the kernel and you won't be able to patch the kernel to make it work on unsupported, newer / alternative user space.