Besides the negative side effects in linux of not having a stable kernel API, is the fact that 3rd party OS's have a really hard time leveraging the opensource

Besides the negative side effects in linux of not having a stable kernel API, is the fact that 3rd party OS's have a really hard time leveraging the opensource work companies do for linux. If the linux driver model were stable enough that a linux driver book was accurate more than 3 months after it was published it would be possible for people to write API compatibility layers for certain classes of drivers and leverage that work in other OSs.