I have Xiaomi Mi6 and it does support ANT+ at least on the hardware level. I was able to pair Wahoo bicycle sensors in the Wahoo Fitness App and they recognized correctly.
The issue is software compatibility. On the previous MIUI version 9 ANT+ plugin caused Bluetooth malfunction. On the current MIUI version 10 ANT+ software (I'm not sure which portion of it) causes unexpected phone reboot upon starting Wahoo software with ANT+ sensors (it works OK in the Bluetooth mode though).
Any plans to fix it for MIUI phones?