Technically my X100 is mirrorless , but I'm sure you mean with interchangeable lenses.
I chose the X100 for it's medium footprint, optical viewfinder, excellent lens and APS-C sensor. Turns out the lens/sensor combination for travel/street photographs is a very desirable combination. I don't mind the fixed focal length lens for what I do. That was a conscious choice that will appeal to few. But within it's limitations, it's a very nice package.
For my usage, the mirrorless market is still shaking out. So much of what I do is low light and quick. I really prefer an optical VF (or at least something effective that's not the rear LCD). My requirements may change in that area with time, re-education, technology and lack of alternative, but for now it's restrictive.
After using the X100, I'm really sold on the APS-C sized sensor. However so much of the mirrorless offering space seems to be be occupied by the P&S alternative crowd, that I don't see much of it left for the DSLR alternative enthusiasts.
I'm not putting down u4/3, I almost bought an Oly, but primarily because they were behind the shrinkage curve. I'm still looking. Small is good for me, just not this, now. Put me down as undecided, it's a political season and maybe the correct Super-PAC can sway me.
Looking forward to hearing others narratives on "Maybe you can tell us and why?".