any way with or without any argument i would like to say following points.
1.if Android 9 need 64 arm xiomi definitely will give it.
2. if that dont want 64 bit one run Android 9 xiomi may be xiomi will not give it.
3. If xiomi consider google stopping support for 32 bit application then definitely xiomi will give the 64 bit one.
4.if xiomi give the 64 bit sys what is the way..?? via ota or flash the device separately?

im not sure untill we get the update..