I cannot say it is battle tested since I use it for personal use only. libvirt with serial console for VMs and netboot for Linux installation (I am not fully netbooting, since I am use netboot.xyz ISO since it is faster than provisioning proper DHCP+TFTP server or setting up a netboot in VM's UEFI). It makes everything much much faster and more comfortable, almost every Linux distro installer works properly over serial (except RH, CentOS and Fedora which say that few options are unavailable in TUI mode). The only think that is needed to be done to make it works is just to provide a kernel option for serial output (console=ttyS0,115200n81).
When I was using RPi more intensively I was using serial (UART) connection as well. No need to switch keyboard, mouse and monitor in case of failed boot or broken network connection. I was just opening serial console on my desktop and possibility of having terminal with Linux on RPi and web browser on one screen, as well as possibility of copying text between two windows was making Linux boot debugging more comfortable.
When I was using RPi more intensively I was using serial (UART) connection as well. No need to switch keyboard, mouse and monitor in case of failed boot or broken network connection. I was just opening serial console on my desktop and possibility of having terminal with Linux on RPi and web browser on one screen, as well as possibility of copying text between two windows was making Linux boot debugging more comfortable.