The RX1 has the potential of offering the best image quality in the smallest package. It's so small and light that I could carry it with me everywhere I go. Until now, if I wanted to enjoy the benefits of shooting with a full frame camera, I would've had to invest in a huge DSLR. That certainly wouldn't be a camera that I'd choose to lug around on a daily basis. I need something light and unobtrusive for that. But everything comes at a price: to achieve a pocket sized, full frame camera, Sony has made some compromises. If the RX1's image quality lives up to expectations and there are no serious handling or performance issues, I'm might just be willing to accept the compromises.
Premium Price and Lens Obsolescence
First of all, you need to pay a premium price for cutting edge technology. Next, the fixed lens design means that the lens will become obsolete with the camera body. Both of these things mean that you'd better get enough use out of the camera so that you feel it's worth the (lost) investment.
I'll assume though that Sony specifically chose a fixed lens concept in order to create the absolute smallest full frame camera that was possible. It's why I'm considering this camera in the first place.
No doubt, sometime in the future a full frame sensor that's optimized for use with M-mount lenses (or similar) will be produced, enabling a very capable and light system - one that's substantially more compact and hopefully more affordable than using a Leica M body. Until then, the RX1 will likely remain the only pocketable camera with such a large sensor.
Most of my photos are taken at “normal” focal lengths anyway, so that's where I want the best possible image quality. 35mm is perfect. The idea of shooting with a single prime even seems liberating: no more fussing with lens changes or zooming back and forth. All that leaves is the decision on how to frame the shot.
There's only one thing with a lens that's permanently fixed to your camera: it's your only lens, so it had better be good. The Zeiss branded 35mm F2.0 lens also has to be up to the challenge presented by the huge, full frame sensor. If it's not, the RX1 fails as a serious photographic tool. If it is, then the RX1 is an interesting proposition in my long quest for ever greater image quality in a compact package.
No Integrated Viewfinder
This is unfortunate for those of us, like myself, who need a viewfinder and would gladly have accepted a slightly larger body to accommodate one. It's hard to see this omission in a positive light; perhaps the fact that the hot shoe mounted electronic viewfinder can be tilted upwards or that you have a choice between an EVF or an OVF makes the lack of an integrated solution somewhat less painful. Unfortunately, adding an external viewfinder of either kind will definitely impact the camera's ergonomics and compactness. At the moment, it's a compromise you need to live with if you want a truly compact full frame camera.
No Tilting Screen
I've stated that I wouldn't buy another camera without a tilting screen. That's how useful I find them. But what the RX1 offers is so compelling that I'm willing to compromise on the tilting screen. I'll get this capability on the compact system camera that I use with lenses that are wider or longer than than the RX1's 35mm.
The RX1 would be my main camera. It's small enough that I can always have it with me when I leave the house. The 35mm focal length is also versatile enough for a majority of my photographs. For outings with photography as the main purpose, or on longer trips, I'll add a compact system camera and 2 or 3 lenses to my kit.
Barring any unforeseen issues with he RX1, I'll likely get one. It'll give me the best possible image quality in a camera that's small enough to take the majority of my photos with.