As far as I can tell the headset itself has nearly no changes at all... A slightly different strap that the controller can stay and minor aesthetic changes. Haven't found any evidence of improved lenses, FOV, etc... I'm thinking I might order the 2016 Gear VR for around $50 brand new and get the controller for $39 when it comes out.
The S8 has a lower PPI than the S6 and S7 had.
I'll wait to see what those users who upgrade have to say.