I have no idea what it is and I’m not sure I even care.
Xiaomi’s doesn’t have any 2K phones, so VR has to be out. Although this is Xiaomi and their rabid fans would probably settle for highly-screendoored VR on their 1920 x 1080 screens.
Replies to the tweet are jumping to the conclusion the above design is a rip-off of Apple design.
Google I/O begins tomorrow.
Next-day update: Miguel Santos in Comments let me know Xiaomi does indeed have one 2K-screen phone: the Mi Note Pro. Somehow that slipped by me. Thanks, Miguel.
May 19, 2016 update: It’s their Mi Box for TV. Meanwhile, they will be among the first brands to offer a “Daydream-ready” (aka VR-ready) phone later this year. But that phone likely won’t be appearing in the U.S. or Europe.
Mike Cane's Atomic Supermen 
Mi Note pro is 2K screen!
You’re right! Somehow that one got by me. Thanks.