Given your comment and the one about having written a stack from scratch twice and regretting it wouldn't in then be a good idea to use just the kernel's battle

Given your comment and the one about having written a stack from scratch twice and regretting it wouldn't in then be a good idea to use just the kernel's battle hardened code but in user space? At most try to upstream some patches so the same code and be used in userspace. All the benefits (well used code) and none of the drawbacks (context switching). Or am I'm hopelessly naive?