ΣAccording to some discussions that take place at Developer / Admin & Moderator level in the official forum of Miui (China) but also in Chat between them, it is stated that from December 1, 2018, it will not be possible to Unlock the Bootloader in Stable ROM from it the date and after.
This will have the immediate effect of not being able to unlock the device to pass Custom ROM, but it will also be impossible to Downgrade to an older ROM due to ARB (Anti-RollBack), and only the Update will be possible in a newer version.
It is not yet certain whether this new policy will be implemented or not, but to discuss it is almost "certain" that it will be implemented even later…
The reason they will take such an action is as they say "Safety Reasons".
I hope this is not the case, as it will again be very difficult for those who receive devices with Stable ROM, to change to a Custom ROM of their choice.
We will inform you about anything new…
UPDATE :
Fortunately not applicable finally all the above according to the official Xiaomi, in a post made on Twitter…
We are providing Unlock Bootloader service and here's the unlocking tutorial: https://t.co/OJwO72LUJp Do not believe in fake news. pic.twitter.com/ISmPeOdLB7
- MIUI (@miuirom) November 22, 2018