So according to PC Gamer, they have a "source" who tells them NVIDIA will be readying it's newest Pascal chips for the mobile form factor and they will be released sometime in August/September of this year. In addition, the rumor is these new GPUs will not be cut down M variants but be full-fledged desktop GPUs crammed into high performance notebooks (e.g. MSI and Clevo) but just clocked lower to fit the TDP and power envelope. That shouldn't really come as a surprise to anyone since NVIDIA crammed a 165W desktop 980 in notebooks last year and with GTX 1070 only sipping 150W and GTX 1080 at 180W, it makes sense to release these as soon as possible.
According to our contacts, Nvidia is readying the release of its new 10-series chips for notebooks. The kick is, they won't be M versions of desktop GPUs. They will be the same chips used on the desktops, just operating at a lower TDP—we're told there will be the same number of shader units, etc.
We're also told that Nvidia will not go back to producing separate M versions of its desktop GPUs, which is good news for those looking for better gaming performance on the road or in a desktop replacement type notebook.
Despite what PC Gamer says, we may yet still see M variants with different names down the line as there are a lot of gamers out there that still want high performance chips but with thinner profiles and longer battery lives but that will probably come sometime after the 1080/1070 are released for notebooks. In addition, we've still got AMD's newest Polaris coming and with the 480 only consuming 150W, AMD could easily shoehorn that into a notebook just as NVIDIA is doing so we expect both companies to announce availability of their newest notebook graphics chips soon.