The OpenThread support for ConBee II (RaspBee II will be next) is currently worked on and in its end phase. Here a new firmware is going to be released together with a new Open Source repository of the OpenThread port. Note this is a standalone Thread firmware so either Zigbee can be run or Thread but not both at the same time. The intend for the firmware is to be able to use the Border Router functionality from a system which can make use of it, like Home Assistant which used a demo board for the Matter demo.
That’s the easy part 
The bigger task is to bring Matter Bridge support to deCONZ, so that existing Zigbee devices are exposed to Matter, as long as the respective device type is supported in the Matter specification. The current developments in the DDF area play a crucial role here, the deCONZ Matter bridge won’t be part of deCONZ itself but a separate process talking to the deCONZ REST-API /devices endpoint and use that to translate from and to Matter. As shown in the Amsterdam event in 2022 controllers like Alexa and co. don’t support Matter bridges yet, I guess that’s also the reason for Philips Hue bridge rolling it out somewhere in 2023.
In terms of our Matter bridge development, it’s in very early stage to get the lowest levels working with encryption. But the biggest question is still in the room: will controllers like Alexa deny communication with devices which aren’t certified, the specification is full of scary walled garden sections that devices need to have certificates which may not work for deCONZ and a zoo of random Zigbee devices.