No, there isn't any officially supported EcoNet devices according to the list in here:
Like I said before, this project, if it succeeds, will be a first for OpenWrt as there is no 'econet' target and no PON port router. The most you will ever get is a SFP-based OpenWrt router from here: https://openwrt.org/toh/views/toh_sfp_ports
But SFP is just a generic expansion port (like PCI-Express) and SFP modules are really just miniaturised routers with potential to host OpenWrt on their own.
As for WiFi 6, it is still in early stages for some manufacturers as ONTs with Wifi 4 is still commonplace for Huawei, ZTE and Nokia.
Someone has worked a build for ZTE F660 in here: OpenWrt now support ZTE F660 V3.0 and HGG420n and as you can see the PON port is still unmanageable. It may take a quantum leap to implement and standardise the a generic PON API (something the likes of dsl_control file) but that's the challenging and exciting bit. (Let's be thankful it's not a Broadcom chipset)