Thanks Vivek.
They're rather differently shaped ... the X2 is longer and thicker in the body, the RX1 lens protrudes much more. Can't say 'til I handle one, but the X2 is already on the verge of being a little small in my hands ... works best with the A&A half case fitted for me; the RX1 might be a little too small for my druthers.
Three things spring to mind that the RX1 will have over the X2: the RX1 has a faster lens on a full frame, so if that sort of DOF advantage is worth it to you there's some gain there, and then higher ISO advantage. 35mm will really be 35mm on the full frame sensor.
Other things will be more subjective, but I bet the RX1 will be more responsive as a whole, and I hope in particular the AF.
1) The FoV on both is about the same.
2) I most often zone focus the X2 with an aperture set around f/8 ... with a wide-normal FoV like this, I'm only rarely trying to get a shallow DoF.
3) It's possible the RX1 might be a little more responsive ... That's another thing impossible to say until you have one in your hand to compare against. The X2 (particularly the way I use it most of the time) is pretty responsive already. When I am going for critical focus at wide open aperture, I'm usually using the EVF and responsiveness is fine.
But the points are irrelevant. My point was that now that I see the new M, I will most likely use the money I might have spent on the RX1 for that, and the X2 is close enough in intent and practice, and good enough quality on all fronts, to satisfy me already.
I'm pretty happy with the X2's sensitivity and noise quality too. See
https://dl.dropbox.com/u/25268645/x2-noise/index.html for my Leica X2 noise test...