My shield adaptor boards arrived last week and tonight we soldered one up.
There is a little bit of dodgy wiring because the ESP-201 had the serial pins in breadboard mode and I couldn't be bothered resoldering them at the moment. But it works!
The screenshot foreground window shows the carambola2 running an MQTT subscriber, reporting clock ticks and version info from the ESP8266, received via RSMB MQTT broker, MQTT-SN to SX1276 inAir9 bridge, and transmitted by the module in the photo.
The ESP8266 is using the deep sleep mode to draw almost no current in between publish events, when it wakes up and (soon) reads sensors and transmits using MQTT-SN via the LoRa module.
Next step is to repeat the test using the Teensy-LC, then write code to read the sensors.