@john.connett, interesting stuff. Yeah, ZigBee protocols being proprietary is will probably cause some license issues.
I recon if you message Harry at Cascoda, you can get in touch with him via GitHub. He should be able to help you know what their radio is really capable of and what support they already have. Here's the link: https://github.com/Cascoda
You would be surprised how much you can achieve with a packet sniffer. If you get yourself a 802.15.4 based sniffer or by using TCP dump on the Ci40, you should be able to sniff some of the packets flowing between your smart meter and it's base station / display. If they aren't encrypted, it will be a lot easier.
Some members of the team a while a go used a bluetooth sniffer to sniff the packets going to a BLE lightbulb. We were then able to mimic the commands and control the BLE lightbulb with the Ci40. Check out this YouTube video here: https://www.youtube.com/watch?v=889R321VysA
In principle, what you are trying to do should be similar.