I would suggest that instead of trying to maintain shared state (which IP addresses are blessed) across all of your nodes, you look into using ipsec. Those internal interfaces aren't for security, they're to segment cheap/fast network traffic internal to the dc from expensive/slow/metered traffic that hits the Internet.
I was wondering, would it be possible to create a better converter that did usb -> rs232/parallel port that had a special driver to put timing info? At least for driving CNC motors with a parallel port, timing is critical, you could send the pulse signal along with a timing, like 1 @ t0, 0 @ t0+1us etc.. Reading would be similar. The chip on the converter would have an accurate clock and faithfully reproduce the desired signal.
After having a quick look at all the external interfaces of my laptop, the only one that has a predictable latency (that I know of) is the microphone/headphone jack. It should be fairly trivial to convert a serial digital data to an audio signal that can be reverted back on the other end. Of course, initially the jack latency needs to be measured (e.g. using a loop connection) and accounted for.
I and most people in my job role carry usb -> DB9 rs232 dongles. doesn't work, of course, if you are trying to set up a serial console to debug the laptop, which is annoying, but it works fine for what we mostly use it for, which is to say, reading other serial consoles.
"Some of the engineers really cared about system performance types of things, so they joined related teams. Some started working on automation [for testing], and they thought that was great—that they didn’t have to do the same thing over and over."
There is still QA, it's just automated QA. Welcome to the 21st century.