It was a very slick design, used one of the AT Megas with 2 H/W serial, and the board design was publicly available. Second version of ESPToy dropped the ATMega, I think they realized it was too much hurdle getting the two mcus so tightly coupled for not much additional value.
Now, Amica, who sell Node-MCU style boards has tried to launch a discussion (both on this site and on the node-MCU/firmware GitHub) on how to evolve the Node-MCU board, which his also open hardware.
IMHO, it would be good to rather capitalize on Node-MCU, which is the de facto 'standard' board for ESP, and has managed to reduce overhead to $2 (Node-MCU sells for less than $5, just $2 above a bare ESP-12 module).
My feeling is that unless you are chinese, you will not be able to get a very low price, which is still the main selling point for ESP. A price point of $10 is too high, for that price you get a Linux SBC such as CHIP, with onboard Wifi, so why bother managing two lower-capability mcus?
I would very much like to see the Node-MCU ecosystem develop beyond the plain board itself, by adding 'shield' capability, and more modularity for the USB/TTL and power options.
Those shields could be ATMega328, or ATTiny85, or a simple I/O mux (74HC4067 provides 16 channel A/D mux for one dollar).
Doing this would cost much less as it is incremental over an already well established ecosystem with several actors, and would be more flexible (IMHO, still...)