I finally managed to get the MX60W flashed, using the MX60 sysupgrade TAR. All BIN files make the ports WAN - tagged with VLAN 2. I used a second device to tag LAN as VLAN 2 and through UART used iptables to allow LuCI on the Meraki's WAN IP:
iptables -I INPUT -d 192.168.xxx.xxx -p tcp --dport 80 -j ACCEPT
I proceed to download/install the recovery and flash the MX60 sysupgrade. I then installed kmod-ath9k and rebooted.
See this page, there's a major documentation issue regarding the MX60's:
The reset button on boot also tries to tftp another image, the Uboot environment needs to be corrected as well.