MIUI 8 Alpha China build has been announced as promised on 1st June for selected devices. Users with Mi3, Mi4 or Mi5 can give it a shot on their respective devices.
But note few things regarding MIUI8:
1- Due to being a Alpha Rom, this ROM might not be perfect for daily usage.
2- Right now only Fastboot build is available, with a flashing tutorial as well.
3- Make sure you do clean flash for error free experience.
4- Public users wont be receiving regular OTAs on this ROM, they have to download it manually when released on forum or wait untill 17th June to get regular weekly OTA, under beta tag.
Thread Link : Check here if your phone supports MIUI 8