The body is smaller, but the lenses still need to cover a FF image circle. If you're traveling with 1-2 relatively small lenses, I can definitely see the benefit. Personally, I usually travel with ~4 lenses covering 16-300mm, f/2.8 on the wider end, including a TS lens, tripod, etc. A smaller/lighter body would probably save <5% weight and not change the bag I'd choose, so there's not a lot of benefit from that, for me.
I do like the idea of a higher MP body that works with my existing lenses. But frankly, I don't really need the MP in a travel body. A higher MP body with all the AF, fps, and ergonomic advantages of the 1D X would be great for birds/wildlife, though.
I do hope Canon continues to develop the mirrorless segment. DPAF is well-suited for that, and I expect that technology will make it to the M line, then to FF dSLRs, and eventually (hopefully) to a FF mirrorless.