I had a conversation with mi chat support today and he confirmed that Kernel source will be released in Jan first week and oreo stable is out and will get notification shortly to update.
below is chat history
I have a question, if fm radio is present in custom roms then why not on stock rom .. i mean dev's if spare some time and provide some solution for this. if possible
Where? Current version is 15.x
its available on forum search before creating new thread.
flash stock boot.img and then probably you will be able to lock bootloader. I have done the same way.