Hello @peter, the EmonTx with ESP8266 adapter you mention is still available Using the EmonTx v3 with the ESP8266 Huzzah WIFI module,
There is the IotaWatt https://shop.openenergymonitor.com/iotawatt
and we are also working on an idea to use the STM32 as a core with a variety of communication options but its some way off at this point, see: STM32 Hardware Development and STM32 Development