Topic: LTE NB-IoT?
First of all, really interesting and smart hive scale! I'm impressed
I'm in Norway, where we don't have Sigfox and LoRa is only in testing in some cities. But we are getting LTE NB-IoT all across the country, which will replace GSM (2G) for M2M communication.
Have you considered supporting this? There are some NB-IoT modules available, such as SIMCom's SIM7000 and u-blox' SARA-N2. Nordic Semi (from Norway by the way) is also releasing nRF91 later this year, which is a very promising module.
LTE's Cat M1 and NB-IoT will be rolled out across Europe and the rest of the world in the coming years, so I think it will be very widely supported in the years to come. SIM7000 even has fallback to 2G if M1/NB-IoT is not available, so that's an option if LTE support is not guaranteed.