FYI, dresden-elektronik is developing an OpenThread RCP firmware for ConBee II and RaspBee II:
It will not make it support multi-protocol like Nabu Casa’s Silicon Lab s Multi-PAN RCP firmware images for Home Assistant SkyConnect (and Home Assistant Yellow built-in 802.15.4 radio), but it will at least allow you to repurpose your old ConBee II or RaspBee II by reflashing it into a dedicated OpenThread Border Router (OTBR).
This alternative ConBee II or RaspBee II firmware is still in very early development, however, dresden-elektronik’s developers have stated their goal is to make this new OpenThread firmware image compatible with Home Assistant’s Thread and OTBR integrations/add-ons, e.i. allow you to form or join a Thread network and make Home Assistant a Thread Border Router:
Thread-based consumer devices use one of the two Home Automation standards: Matter or HomeKit. So in the future using this OpenThread RCP firmware on a ConBee 2 or RaspBee 2 adapter will allow adding Thread-based device directly to Home Assistant, using the respective Home Assistant integration: