It would be great to support the new Sonoff S31 smart plug!

There are a number of cheap wifi controlled outlets for $20 or under, but the S31 is compact (two can fit on one US duplex outlet), supposedly capable of 15A, and most importantly does energy monitoring!
And several sources are offering it for under $17, shipped.

See the last photo on this page: [(https://fccid.io/2AE2J-S31/Internal-Photos/Internal-Photos-3692513)]

I'm guessing that it continues to use the ESP8266 (or ESP8285).

It looks from the FCC registration photo as if there are pads (perhaps thru hole if not filled with solder) for VCC, GND, TX, RX and D_TX, D_RX (whatever the latter are).