First, you seem to forget that Core M isn't anywhere as integrated as a typical mobile SoC. It still carries its separate chipset and most likely needs a lot of peripheral ciruitry as any PC platform does. It's more a shrunken PC platform than a mobile one.
Secondly, the rumor still isn't substantial at all. Just concluding from "Brian Krzanich didn't mention Broxton lately" to "Intel is giving up mobile SoCs" is more than a stretch. It's pure noise without any base.
I disagree there. Laying out by hand makes sense especially for high speed designs. For mobile, where power and density is most important, synthesis makes more sense (and especially is easier to do). The issue with Core X is that it needs quite a lot of space on die obviously. That's good for the high end PC market but not for mobile. Another core makes sense there.
Having said that, Intel could just take their digital design lead with all the tricks they already use in Core X and integrate it into a mobile SoC. I hope Broxton is just that.