I have published a rewrite of the I2C subsystem that should solve the I2C stability Issues, It is NOT a drop-in replacement for Wire(). There are hardware differences between the AVR and ESP32 that require a different strategy.

It is a ALPHA TEST version, DO NOT use it in ANY PRODUCTION ENVIRONMENT.

To try it you can simply download the zip and OVERWRITE your arduino-esp32 sdk.

This fork is base off of espressif/master from 11/11/2017
It changes:
cores\esp32\esp32-hal-i2c.c
cores\esp32\esp32-hal-i2c.h
tools\sdk\include\soc\soc\i2c_reg.h
tools\sdk\include\soc\soc\i2c_struct.h
libraries\Wire\src\Wire.cpp
libraries\Wire\src\Wire.h
README.md

stickbreaker:arduino-esp32

Chuck.