I have yet to read anything specific that is different between the two, other than the enclosure being plastic versus aluminum. Whatever the difference, the design changes are aimed at helping the Wookong to maintain altitude better.
I fly the IMU V1 with no problems at all on my S800, and I can promise there are still thousands of MRs out there flying WKM with V1 on all sorts of MRs, including S800s. Remember forums tend to be a place where people work out their problems, not proclaim successes. I understand your concern, but just sayin'...