I2C is supported pretty well on former Omega2 firmwares.
Only the i2cdetect command didn't work up to the firmware v0.2.2 b194.
The i2cdetect command is a part of the 'i2c-tools' package, it's a separate utility: /usr/sbin/i2cdetect.
You could live without it.
An evergreen question ;-)
Older Omega2 firmwares:
Newer - OpenWrt 18.06 based - Omega2 firmwares:
Omega Firmware Changelog (Omega and Omega2):