I have been, and continue to be, tempted by the A7. The increased dynamic range, resolution, and lack of crop factor with legacy lenses are all really appealing to me, and the grip and control layout feels really good in my hands. I like having the 3 command dials, and an exposure compensation dial that works in M mode with auto ISO. That's important to me!
But there are a bunch of other issues that I find extremely disappointing. I'm not tremendously concerned about the lack of native lenses, because I can't justify spending that kind of cash on their fairly humdrum AF lenses (the 55/1.8 being the only standout in terms of quality). As a result, the quality of their manual focus features are really important. I found that the focus peaking on the A7 was actually really poor. I only tested it with the kit 28-70, but even that should be sharper than most legacy lenses, so it should be representative of its abilities. I found that depending on the settings (high/med/low) it would either be full of false positives (high), or when magnified (low), wouldn't show any peaking at all. On top of that, the lack of a touch-screen for setting the magnification point means that in practice, manually focusing with the A7 seems to be no faster than with my GX1 that doesn't even have peaking. Compared to the GX7 which let me quickly and reliably get focus using a combination of peaking and touch magnification with my old Takumar 50mm/1.4 even wide open, it's a lot harder to justify.
The other thing is that the low-light performance of the A7 was actually not as big an improvement as I expected, either. I would say that at the high end, it would let me squeak out one more usable stop compared to the GX7 (12800 vs. 6400). It's noticeably cleaner at ISO 3200 and more moderate shooting conditions, but I'm not that noise averse as long as it's relatively fine-grained and "filmic." It's only when noise starts getting really blotchey that I'm going to disappointed. There's a point at which "low light" simply becomes "bad light" and while you may be able to get a acceptable documentary image with a larger sensor, it's never going to be something pretty.
The other thing I'm disappointed by with the A7 is the lack of any sort of quiet shutter capability. Not the biggest deal, but definitely nice to have.
All in all, it's looking like my next upgrade is likely to be a GX7 rather than an A7. Which is kind of disappointing. We'll see if I can get away from pixel-peeping low ISO static images, though, which is where the A7 walks away from the GX7. I do a fair bit of shooting in those conditions, so even if the focussing is slow and I need to approach the camera more like an old medium format rig, maybe the output is worth it. Never an easy answer...
Though in that case, I might also be strongly tempted by just getting the GX7 and a used Sigma DP1 Merrill for the static detail stuff. That might be a happier compromise in the long run, even if it doesn't really address low-light situations.
