Please consider making your RF-Bridge work to the new Sonoff Zigbee Bridge (Sonoff ZBBridge) including using the Zigbee radio to control Zigbee devices
Itead has just launched Sonoff ZBBridge as an inexpensive Sonoff Zigbee Bridge which is based on a similar design as the Sonoff RF Bridge 433 (which obviously your firmware already has support for).
According to the teardown on notenoughtech.com it sounds as if it is based on Silicon Labs EFR32MG21 (EFR32 Mighty Gecko) for Zigbee 3.0 radio module support and ESP8266 (ESP8266EX) for WiFi and bridge/gateway/controller software
Tasmota firmware does something similar with Zigbee2Tasmota but by connecting an ESP8266 to a Texas Instrument CC2530 module instead however it too is using a serial communication protocol, see:
EZSP (EmberZNet Serial Protocol) interface that Silicon Labs uses is also well documented and already used by open source projects, see example Home Assistant's ZHA integration component via zigpy and bellows:
Please consider making your RF-Bridge work to the new Sonoff Zigbee Bridge (Sonoff ZBBridge) including using the Zigbee radio to control Zigbee devices
https://www.itead.cc/sonoff-zbbridge.html
Itead has just launched Sonoff ZBBridge as an inexpensive Sonoff Zigbee Bridge which is based on a similar design as the Sonoff RF Bridge 433 (which obviously your firmware already has support for).
https://www.cnx-software.com/2020/04/16/sonoff-zbbridge-wifi-to-zigbee-gateway/
According to the teardown on notenoughtech.com it sounds as if it is based on Silicon Labs EFR32MG21 (EFR32 Mighty Gecko) for Zigbee 3.0 radio module support and ESP8266 (ESP8266EX) for WiFi and bridge/gateway/controller software
https://notenoughtech.com/home-automation/sonoff/sonoff-zigbee-bridge-preview/
From the images it even looks like they are reusing the same injection moulds as for the Sonoff RF Bridge 433 housing/enclosure
https://sonoff.tech/product/accessories/433-rf-bridge
https://www.itead.cc/sonoff-rf-bridge-433.html
https://www.itead.cc/wiki/Sonoff_RF_Bridge_433
Tasmota firmware does something similar with Zigbee2Tasmota but by connecting an ESP8266 to a Texas Instrument CC2530 module instead however it too is using a serial communication protocol, see:
https://tasmota.github.io/docs/Zigbee/
EZSP (EmberZNet Serial Protocol) interface that Silicon Labs uses is also well documented and already used by open source projects, see example Home Assistant's ZHA integration component via zigpy and bellows:
https://github.com/zigpy/bellows
https://www.home-assistant.io/integrations/zha/
https://www.silabs.com/community/wireless/zigbee-and-thread/knowledge-base.entry.html/2017/05/25/build_an_ezsp-spiho-2VE8
https://www.silabs.com/documents/public/user-guides/ug100-ezsp-reference-guide.pdf