So, I was curious enough to take one apart finally, and it seems at least the EU v2 is using a 8071A.
Serial is 1.8V, from left to right (vcc, ground, rx, tx)
Boots straight with atleast the Xiaomi x3600 and redmi ax6 initramfs, with functioning wifi on both radios.
Have been trying to clean up the dts and to build the ipq-wifi package for this model, but here is where I'm struggling.
I have dumped the art partition and I believe I should have a working board-2.bin, but all I get is an empty apk when I compile the ipq-wifi. I've tried placing the file in as instruced by the makefile, but no luck.
wip repo
Well, it seems I should have posted here hours ago, would have saved the afternoon 
The naming was inconsistent, and it seems I have to copy the firmware file to the build dir / ipq-wifi directory. Now the apk contains the necessary files and it seems to work, at least for a test.
ls -R ipkg-aarch64_cortex-a53/
ipkg-aarch64_cortex-a53/:
ipq-wifi-tplink_deco-x60-v2/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2:
lib/ rootfs-overlay/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/lib:
apk/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/lib/apk:
packages/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/lib/apk/packages:
ipq-wifi-tplink_deco-x60-v2.list
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/rootfs-overlay:
lib/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/rootfs-overlay/lib:
firmware/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/rootfs-overlay/lib/firmware:
ath11k/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/rootfs-overlay/lib/firmware/ath11k:
IPQ8074/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/rootfs-overlay/lib/firmware/ath11k/IPQ8074:
hw2.0/
ipkg-aarch64_cortex-a53/ipq-wifi-tplink_deco-x60-v2/rootfs-overlay/lib/firmware/ath11k/IPQ8074/hw2.0:
board-2.bin
