Ethernet is nice, but for low-level debug purposes, it is significantly harder to use than UART. With UART, you have a single integer to guess, maybe one of th

Ethernet is nice, but for low-level debug purposes, it is significantly harder to use than UART. With UART, you have a single integer to guess, maybe one of the 10 options. And guessing it simple, as data flows even when nothing is connected, so you can trivially find it on the PCB and scope it. With Ethernet, you have vastly more thing to guess. Starting with Ethernet pinout, then IP address, then port, protocol and authentication. And in most cases, you are not going to be able to passively listen and get useful debug information - while I can theoretically imagine an embedded system configured with netconsole in broadcast mode, I've never seen such configuration in practice. Yes, Ethernet is very nice if device works, but it's pretty unusable for embedded / early boot debugging.