First of all, Bind Mi Band works on Windows 10 Mobile.
If after upgrade from 8.1 the app can't find the band, try next steps:
1. Remove band in Bluetooth settings (actually remove, don't just click on it) and then add it back. Later you will need to bind band in the app again and it should work.
2. If the first step doesn't help you, try to reinstall the app. But do step 1 before that.
Also, answering the question if something changed with notifications in the new OS: no, nothing has changed in Windows 10 Mobile. We still can't make band vibrate when an incoming call is ringing.
So this is all.
There will be more news soon :)