A few days ago the stable release of the MIUI ROM based on Android 6.0 Marshmallow was released for the Xiaomi Mi 3, Mi 4, and Mi Note in China.
As of today, the stable Marshmallow-based MIUI 6.3.17 is available in Global Beta and can be installed on the Xiaomi Mi 3, Mi 4, and Mi Note outside China.
Being a global ROM means the devices outside China can use Google Play Services and Play Store.
Xiaomi Mi 5 was the device to introduce the Android Marshmallow with MIUI 7, but Xiaomi seems to be working hard on bringing the update to as many devices as possible.
Thank you, Sagar, for the tip!