LinuxCNC-PC - Remora - OrangePi3 LTS - BTT SKR V1.4 Turbo

Well I’m always up for a challenge!
I reckon I can get this running as reliable as ever.
This was the best solution I could think of, as usb isn’t an option. Then realised, this has the potential of actually being quicker and more reliable than usb.

Go for it!
Despite Tuxcnc being right about the time and effort, humanity would not reach very far if it did not try stuff that may or may not be "standard".

I wouldn't do this, but I'll follow the topic as I'm sure I'll also learn something. Personally, I would have tried to run LinuxCNC directly on the OrangePi3. Or added a W5500 to the SKR.

A couple of months ago, I did some tests with Remora and a RP2040; I watched Rod's video on Youtube to achieve real time performance on the ethernet connection between a Pi400 and the Pico. My guess is that you'll have to compile a real time kernel for the Armbian OS too (did it last year for a Radxa Zero 3E, worked more or less).

Yes running Linuxcnc on the OrangePi would be easier. And the board would probably run it extremely well. But again, that’s normal. 
if I’d opted for the w5500 on the SKR, I’d have to have ported the code over from the stm32/rp2040 side of things. Not hard, but not as challenging as this.
So I opted for this. Means I still have the main pc doing all the hard legwork, and the OrangePi just bridging the traffic over to the SKR. Which I think long term, is the best option, performance wise. This was the SBC isn’t doing a lot of work at all.

the last time I did anything challenging, was when I originally bought up Armbian for the OrangePi 3 LTS. This was nearly 5 years ago, and it’s the same board I’m using today! Never found a use for it! I had it running klipper and a 3d printer for a while 

You should be able to build a PREEMPT_RT image using Armbian for the OrangePi and install LinuxCNC and XFCE on it. I have done this with a Odroid N2+. I would go that way and ditch the PC out of the equation.

In the build process, you just need to run menuconfig to configure the PREMPT_RT flags.
Start here  docs.armbian.com/Developer-Guide_Overview/