I have been working to test the ESP32 (with a lot of help from the Arduino core team!) and I have tested a variety of I2C sensors. A repository of Arduino sketches for these sensors (MPU9250, BME280, MS5637, VEML6040, BNO055) as well as sketches that make use of the other ESP peripherals known to work can be found here:
https://github.com/kriswiner/ESP32
I will add more sketches as my testing continues...