Bootloading should also work with half-duplex communication. Its just that there is no example for that (AFAIK). So you would need to write your own bootloader component.
The physical layer of RS485 vs 422 impacts the transceiver
signaling, hence firmware. See en.wikipedia.org/wiki/RS-485
So you would have to modify UART APIs put a firmware wrapper
The current UART bootloader is for full duplex mode. There are a couple of modifications needed for the half duplex mode.