Geilo, after days of trying to figure out how it works, I finally got a Xilinx axi_uart16550 behind a PCI Express endpoint to work as a practically auto-detected tty on Linux, modifying the 8250_pci driver.
So, now there's /dev/ttyS4 directly talking to a #neorv32 softcore #riscv MCU on an #FPGA.
Now, to clean-up and understanding what I've actually done.
