I see what you mean. Yes, there are counter examples of kernels that can be compiled without extensions. With my rough knowldge of the Linux kernel in particula

I see what you mean. Yes, there are counter examples of kernels that can be compiled without extensions. With my rough knowldge of the Linux kernel in particular, I imagine there are a few places where the use of extensions makes for much better code than without, and for those places the change is of debatable utility. However, extensions are the rule rather than the exception for the kernel. The bulk of the kernel could be written without them.