It looks like Nikon is planning to introduce its new Phase Fresnel technology to some popular focal lengths. A newly discovered patent shows a Nikkor 24-70mm f/2.8 lens with a Phase Fresnel element.
The patent was discovered by Nikon Rumors and originally filed back in May 2014.
PF technology would make the new 24-70mm f/2.8 significantly smaller and lighter than its predecessor. When the Nikkor 300mm f/4 received a PF element, it became 1.5 pounds lighter and 30% shorter than its predecessor.
A Nikkor 24-70 f/2.8 VR has already been rumored for quite some time now. If PF and VR were to arrive in the 24-70mm at the same time, that would be a pretty significant announcement in the world of Nikon gear.
In related news, a different Nikon patent filed back in 2012 also suggests the company is planning a 200-400mm f/4-5.6 PF lens. There are also recently discovered patents for a 16-30mm f/4.3-5.6 and a wide angle (10mm or 17mm f/4) tilt shift lens.