FYI, from the comment here by konistehrad related to ZHA Device Handlers version 2 (ZHA-Quirks V2) architectural design developer discussion it sounds as he now has some time again to continue working on his ZGP pull request for zigpy:

How to integrate ZGP devices into V2 Quirks? · zigpy/zha-device-handlers ·...
I've been working steadily on adding ZGP support to Zigpy for some time, and I'm now finally able to dedicate (a little) time to completing the project. Since I've been gone we've received an entir...