Submitted for people's discussions and thought:
https://github.com/martin-ger/esp_wifi_repeater
This is slow and very limited - I'm seeing that it is limited to 8 stations, peaks at ~5 megabits, and I'm sure that the range is very limited without a separate antenna/amp. However, ESP8266 is ridiculously cheap; it's a few dollars for the chip itself, and maybe $8-$9 for the NodeMCU built on it, probably less in bulk. In light of that, perhaps there's a way this can be used in some fashion as a component in a meshnet.
-Chris