MIUI 10 Beta Global on Mi Max 32 Hydrogen:
I took the plunge to play with the Beta ROM's, and to say the least, I really like what they intend with MIUI 10, below a brief review.
For starters, they are designing around big screens now

it no longer looks like a small phone screen enlarged to fit the bigger screen. Side by side comparison, font and icon sizes are almost the same, but they are fitting more icons onto the screen, you can view more info, eg contacts. Now the big screen phones will look a bit more "professional" looking, giving you a sense of feeling, that you have indeed bought a big screen phone
For now MIUI 10 is based on Android 7, I'm hoping this will be on Android 8 when it becomes out of Beta.
Calculator has some improvements done to it.
Swiping from the bottom brings up a Search screen.
I get the sense, the finish in the GUI is kinda like mimicking the Apple GUI, kind of a bit a fresh air compared to the old 2D look.
Battery drain is comparable and acceptable.
Swiping from Left to Right brings up the common tasks etc, as in MIUI 9 but more refined in the GUI.
These are the changes I have been able to observe so far and I'm liking it. In fact, I'm liking it more than I did going from MIUI 8 to MIUI 9. I am using this ROM as a daily driver and I have not had any issues with it so far being so young in Beta. All my favorite Apps and Games play just nicely, no hiccups.