Rumors point to an early 2016 launch and even a Snapdragon 820 SoC.
http://www.notebookcheck.net/Asus-PadFone-S2-could-be-coming-March-2016.146766.0.html
No, no, no~
Why make it a 5.5" phone? They already have the Zenfone 2 for that size. This phone will be docked to a tablet if extra size is required, so I really think making it a phablet make sense.
For the tablet dock, I do wish they make it compatible with the previous version of Padfone X/S, so that more people will likely to buy it. My suggestion for the tablet is it should come with a large >7000mAH battery, smaller bezels (far, far smaller bezels), front facing stereo speakers, and a 2K screen res (well, I don't mind if this actually stays at 1080p to be truthful)