If they release Project Treble GSI with MIUI then can update any device to MIUI with latest android.
New and many old devices have support PT.
After update on MI5 i got bootloop too.
Some questions to who updated and boot system normal:
1. what version do you have before update
2. when your last time wipe /data or full reconfig . Clear system or very dirty.
3. Enabled/Disable lockscreen password/security (maybe we must disable and...