The 'ESPloit v2' [1] appears on USB as both a keyboard and a serial port, and any data sent on the serial port can be exfiltrated by the ESP8266 over its own wifi connection.
You can also imagine a loop where first you install a keyboard logger and exfiltrate the user's password, then later you want to update the exploit scripts to make use of the password. Or hell, maybe this is a prank product and having a wireless button to rickroll your victim on demand makes you laugh.
With that said, the first person to make a fake USB keyboard had a much bigger and more exciting trick than this incremental change.
Edit: Or to put it another way, this is like the NSA's "Cottonmouth" bug, which "will provide air-gap bridging, software persistence capability, 'in-field' re-programmability, and covert communications with a host software implant over USB" [2] but 10 years later and without charging a million dollars for 50 units.
Long story short, underclocking the ESP12 compresses the RF envelope for 2.4GHz . It also means the RF energy is in what looks like 1/3 a normal 2.4GHz channel.
The awesome side effect is that this device's SSID is completely hidden from regular 2.4GHz radios. You need another ESP12 with the same underclock ratio... and then need the SSID (if hidden), and the password.
You'd be able to find it using an ADALM-PLUTO. It'd stick out like a sore thumb, but it still wouldn't make sense what's going on unless you build a decode stack in Gnu Radio.
