Xiaomi's last device with a MediaTek SoC was the Redmi Note 4. The MediaTek Redmi Note 4 never attained the critical acclaim of its Snapdragon sibling but it would seem the Chinese company is set to make a return to its old MediaTek ways.
https://www.notebookcheck.net/Xiaomi-has-MediaTek-Helio-P60-P70-chips-lined-up-for-its-2018-devices.293638.0.html