I understand they have slightly different use cases, with surface pro 4 being a tablet that can act as a laptop, and surface book being a laptop that can act as a tablet. But I can't get over the feeling that they are almost two halves of the same "ultimate" product, as though there is a missing SKU in-between them. Looking around at competitor's me-too devices, pretenders to Surface's throne, no one else seems to have hit upon the missing SKU either.
I'm talking about a theoretical device I call the "surface book pro". Combining the best of both surface product lines into a machine with no compromises. Spro4-like device with a USB3 port and kickstand built into the tablet's body, but which has a surface book-like detachable 'hard' keyboard (with extra battery and dedicated gpu in it). You wouldn't necessarily have to launch a fifth surface product line (alongside surface 3, pro, book and hub), if there was a way to make both the spro type cover and the sbook cover be able to connect to the same top half tablet, then it would just be a matter of the user choosing the keyboard type that is right for their needs.
I'd also like it to include LTE like that one outlying configuration for... I believe it was the Surface Pro 2. This would allow increased portability with the 2in1 tablet/laptop, compared to currently, where it is confined to acting more like a laptop only, in wifi enabled areas.