I agree, "Next" means it can't be related to any existing hardware. It has to be something new. My guess is that it won't be 1 single thing or device but will be WOA and a handful of devices running WOA. A laptop, a 2 in 1, Maybe some Surface Pro like device from another OEM. And, if there is going to be a surprise, it will be a 8" or so Surface Mini running WOA. Devices with phone capabilities is what they are moving towards so WOA has to be what is "next".
We know about Windows S, we know about Surface laptop, we know they aren't making any actual phones and we know it can't be related to any other line of devices or software we already know about. There is nothing left but WOA and devices running it. The firwt line of devices that will be released end of year.
That's a reasonable bet, unless its out of left field, WoA is all we know about that's left.
I was think about this last night actually. They kind of need a mini. While some people will certainly like always connected data services and GPS on a laptop, it only really shines if its portable. That means 6-9 inches. Something shoulder bag-able, purse-able, even jacket pocketable.
Even then its niche for use a phone - productivity users, and people who insist on decent screen real estate.
I was thinking it would be best if they could pack as much as possible, in terms of functionality in such a device, as to increase its appeal - depth sensors for AR, dual microphones for homehub/Cortana, fantastic audio for media playing, a little keyboard attachment for productivity.
8 inches or smaller really I think could also use cshell. That form is a little cramped with win32's without a stylus. It's useable but not idea.
Of course its the OEMs that will really sell the idea of WoA on tablets, hybrids and notebooks, but history shows they are more followers than leaders. Take existing windows on tablets - virtually no one main an 8.9, or 9.7. They started trying 8s, and when that fizzled, they copied the surface.
Whatever MS produces in terms of a demo device, is quite important - it needs to show OEMs how to make windows more mobile. It needs to be other than just a surface - no one is going to ditch their phone for something as big as a netbook. And if they have a phone, why use LTE/calling/GPS on their laptop much at all?