Resources available to dilute the rt, kernel and user-space boundary

The good news - Linux has all the concepts available that one would need to at least massively reduce the expense of kernel-space user-space crossing. The core issues here are

• zero copy strategies by mapping memory between kernel and user-space
• kernel_threads, running applications in the kernels memory space
• source code availability allowing to add your own system calls easily or modify the kernel to fit your device better.
• open technology - the underlying concepts in the Linux kernel are well known and documented thus the repertoire that is available to the programmer is enhanced

Its all there - it just needs to be used.