Vivo finally confirmed another phone. The device is called The XPlay5 and is said to be the successor to the Xplay3S (launched in 2013). It is also rumored the handset will feature a dual-curved display.
As for the specs, they were revealed on a recent Antutu listing:
the core of the device is a Snapdragon 820, quad-core
5.5-inch QHD display
4 GB of RAM
16 MP rear camera
8 MP front shooter.