Remora for RK3588 Boards

Yes, that's true. But there are breakout boards available for it that already have LAN on board. For making steps in realtime this would be also more than enough.

The Orange Pi 5 was not known for me, but it sounds really interesting.
One could implement remora on the Orange Pi 5 and use that as stepgen and finally it would have enough power for driving fancy displays

After all, in my opinion it is better to have a system composed of multiple simple parts, than a large monolith. With a monolith you depend on the provider of the monolith.

Now you can use a standard x86 PC with any remora enabled card. You are free to replace either the one or the other.
Do you need GPU for watching youtube while machining? No problem.
A second network interface? Just insert a new network card.
This is a huge benefit especially for open source community.

Yes, an STM32 would be the first choice, if it is available again.

Yes, maybe "remora" name should be reserved for projects that use an external MCU interfaced over SPI (or Ethernet) to LinuxCNC. Using an integrated MCU seems cool, but it's not clear how it is interfaced (shared memory maybe?) and how is firmware flashed to it. This is something that was already done in the past with  allwincnc project . Hard to say if similar approach is applicable to RK3588 with it's integrated Cortex-M0 core.

Until this is investigated, Remora can be used with RK3588 with an external MCU. It's SPI implementation is using bcm2835 library which will only work on RPi hardware. When porting Remora to UP Board, Mr.Bubbles rewrote this SPI code to use spidev (should work with RK3588 as well as any board with SPI kernel driver), however this implementation appears to have  realtime performance issues .

So finally, it leaves us with Ethernet. Will it work? Most likely, yes. Anyone already tried it? I don't think so.