The rectangular camera is supposed to be equipped with advanced lenses that allow for 5X / 50 X digital magnification and it may be paired with a 108 MP sensor that is capable of 8K @ 30 fps video recordings. It is expected to be featured in one of Xiaomi's flagship model launching in 2020.
https://www.notebookcheck.net/Xiaomi-patents-rectangular-zoom-camera-design-for-upcoming-handhelds.441308.0.html