Here are the sizes compared:
The link:
http://camerasize.com/compact/#624.393,639.496,557.479,ha,t
If size and weight are the main criteria, Sony wins comfortably. It's much smaller and at around 1 kilogram weighs half of what the Leica and Nikon alternatives do. However, since I've already chosen the Nikon over the Sony, I apparently don't care to much about that. Important also is that the Leica lens has more reach than the Zony and is a stop faster at the wide end.
I remember an interview with a lens designer a few months ago, can't remember who, who said that by making a lens constant aperture, they always give away around one stop at the wide end. Zoom lenses are naturally faster at wide angles, but they limit that to make them constant.
The debate about this lens reminds me a bit of the debate around the PanaLeica 14-50mm f/2.8-3.5 for 4/3, a lens that I have and love dearly. It's a monster compared to the tiny 4/3 format, although only half the weight of this lens. It is however the best zoom lens I've ever used, always sharp corner to corner, regardless of aperture and focal length. And it's a great range, usable for interiors and great for portraits too. In reality, the only lens I need 90% of the time.
If I were to buy into this system, which would require financial luck of epic proportions, the three lenses currently in the program might be the only lenses that I need. One for general use, one for air shows and sports (if the viewfinder and AF can live up to that kind of use) and one for wide apertures. Most of the time, I would only carry two of them, and possibly an adapted telephoto prime. The Zeiss 21mm can obviously also be adapted.
I understand the argument about weight. Many of us are past 60, and I'm getting closer myself. Still, I don't have a problem with heavy stuff, and use the good, old 80-200 AF-S hand held regularly. Maybe Leica didn't target old folks with this camera, but see it as what they think the new generation of professionals need. It has the "modern look" to complement modern designer gadgets, and although many complain about the grip, it can't be worse than the first generation A7, which basically didn't have one.