I found an ESP8266/ENC28J60 dedicated lib that directly replaces the standard one...
I have one of these Ethernet breakout board, and I plan to make it work with my esp8266 d1 mini board..
The advantage of this lib is that it seems to wrap also a better stack, which liberates a ton of memory ...
My plan is to try to build a bridge with the ESP/enc combo...
The Ethernet will supply wireless com to otherwise Ethernet only enabled devices... Well, it's a plan... Not sure if doable at all, but the hardware exists...