Hi,
As an experiment I edited arch/arm64/boot/dts/marvell/armada-3720-community.dts to change the name of wan to wan1. I then recompiled the kernel and copied the new armada-3720-community.dtb into /boot on the espressobin. Rebooted and the interface is called wan1 now, and works fine.
Just keep in mind that the armada-3720-community.dtb is kernel-specific, so you should follow the instructions on compiling your own kernel and use the armada-3720-community.dtb and Image.
I don’t know what the other settings in the dts do though!