> It's been very reliable so far, but sooner or later it's going to start failing.

It's not going to start to fall. The whole reason why serial port is there is to be the fallback access if everything else. It is a dumb and simple protocol, doesn't need any network to be configured.

I don't understand how serial is instead included in the complexity of networking, easily losing access if you accidentally bring down the interface or forgetting the IP.

You can't debug kernel boot because there is no networking when the kernel just started.

I think it's just obsession on complexity coupled with cutting down cost.