Maybe also worth taking a look at the Zigbee Shell / CLI wrapper for Nordic Semi nRF5 family of NCP as a reference?

[Hedda]

Nordic Semi who makes nRF5 series of multi-protocol chips have a Zigbee Shell / CLI wrapper might be worth a look for reference?

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/zigbee/shell/README.html

Their arguments for going with the CLI Zigbee architecture they did in this command shell is shortly described here:

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_tz_v4.1.0%2Fzigbee_architectures.html&cp=8_7_0_3_2

Nordic Semiconductor has this quick reference with commands supported by their Zigbee CLI:

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_tz_v4.1.0%2Fzigbee_example_cli_reference.html

And examples for Zigbee NCP:

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_tz_v4.1.0%2Fzigbee_only_examples.html

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_tz_v4.1.0%2Fzigbee_example_cli_agent.html

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_tz_v4.1.0%2Fzigbee_example_cli_agent.html&cp=8_3_3_8_5_1_0&anchor=zigbee_example_cli_agent_interfaces

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_tz_v4.1.0%2Fzigbee_example_ota_examples.html

It also includes a sample implementation of how their Zigbee CLI can be used for the implementation of a Zigbee-MQTT gateway:

https://infocenter.nordicsemi.com/topic/sdk_tz_v4.1.0/zigbee_cli_wrapper.html#zigbee_cli_wrapper_mqtt

There is also this real-world example of a project implementing a slightly older version of that Nordic Semi's Zigbee CLI wrapper:

https://github.com/hipiphock/Dongle-Handler/ (and related https://github.com/ninima0323/TestGUI which uses that handler).

FYI; nRF52 series and nRF53 Evaluation Kir and Development Kit hardware for nRF Connect SDK is relatively inexpensive to buy:

https://www.nordicsemi.com/Products/nRF52840

https://www.nordicsemi.com/Products/nRF5340

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/ug_nrf52.html#ug-nrf52

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/ug_nrf53.html#ug-nrf53

Note that their NCP solution for nRF52/nRF53 (nRF52840/nRF52833/nRF5340) has now reached a v1.0.0 milestone in NCS v1.7.0:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/releases/release-notes-1.7.0.html#zigbee

PS: Most of the links comes from https://github.com/zigpy/zigpy/issues/394 which is a request for nRF5 Zigbee radio library for Nordic Semi nRF52 / nRF53.