Ever since the RX100 came out and got stellar reviews, I"ve been following it. It's recently dropped in price a bit and my wife is willing to let me get one but ONLY IF I am willing to part with my EOS-M.
My recent purchase of an SL1 was already making the EOS-M a tad redundant, so I am considering this trade off.
My plan was to keep my EOS-M with just the 22mm without building out the system, basically using it as a fixed-lens camera (a crop sensor RX1, if you will). This combo did wonderfully during a vacation earlier this year, and has been very reliable, and I enjoy the 35mm equivalent FOV. The only things I feel are lacking is I wish the AF was a tad faster sometimes, and I do miss a zoom lens at times as well.
I recently got a chance to borrow a RX100 and shoot it for a day, and I was impressed. The stuff about the excellent IQ seems legit. To my eyes in my usage (which I guess is all that matters) the EOS-M does have a slight advantage in IQ, and about a 1-stop advantage in low light (I'd probably only shoot up to ISO 1600 on the RX100, on the EOS-M it's 3200 easy).
What the RX100 has going for it is obvious - zoom lens, built-in flash, and the AF seemed a bit snappier.
What I was really surprised by and gave the RX100 a big advantage was the compactness. I didn't think it would make that much of a difference from the EOS-M over a day's shooting, but it did. To me the EOS-M, even with the 22mm, is not a pocketable camera. And because of it's weight, I don't feel comfortable with it on a wriststrap either (tends to swing around too much, so I'm worried about it bumping something). It's a small bag/shoulder strap type of camera, albeit an amazingly small one. The RX100 was pocketable in my jeans, and carrying it around all day on a wriststrap was a piece of cake.
So there it is. That's my thought process so far. I know this forum will probably sway Canon, but I still would like to hear opinions.
TL;DR - Deciding between EOS-M /22mm vs Sony RX100. EOS-M has IQ advantage, RX100 has size advantage. Just got SL1 so EOS-M may be a bit redundant.

