Got the A6700 housing. It arrived too late for me to take it to my most recent liveaboard trip - in fact, it was delivered the day I got off the boat - and I haven't taken it diving yet, but I've been playing with it dry, and it's quite interesting.
It's a tiny bit shorter and narrower than the A6xxx Salted Line housing - almost imperceptible; I only noticed the difference when putting the two housing backs against each other. It is quite a bit deeper, however, to accommodate the A6700's big grip I suppose, so considerably more total volume.
The ergonomics are an eclectic mix. As can be seen from product photos, there is no AF-ON thumb lever for back-button focusing, and the shutter trigger is set up to be operated from tray handle. However, I seem to be having issues operating it for shutter half-press - most of the time, I end up doing a full press when intending to do a half. On the other hand, if I forgo the tray grip and hold it by the housing, I can operate most camera functions without moving my right hand at all, which was quite a surprise! I don't have large hands, but I can grip the housing fairly comfortably, with my index finger on shutter trigger, my pinky on the bottom knob (operating the front dial), the ball of my thumb on the rear knob, and my thumb a short movement away from the top knob. I have the camera set up for shutter speed on rear dial, aperture on top dial, and ISO on the front dial, so this lets me adjust aperture with the tip of my thumb, shutter speed with its base, and ISO with my pinky, while zoom is controlled by the fingers of the left hand over the tray handle. The AF-ON button, in this configuration, is within easy reach of the thumb, as is FN and the five-way controller, although playback button if a bit of a reach.
The viewfinder seems a little different; it's a bit longer and the eye pad feels more securely attached. The old one (on A6xxx) was almost useless, and the eye pad fell off and was lost within a couple dives - I'll see whether or not this one is any better, although I don't have high hopes.
There is no screen shade or pegs for one, so my method of attaching the Nauticam screen magnifier hood is no good anymore. I'll have to 3D print a pair of rails and glue them to the housing. The longer viewfinder will require cutting out an even bigger piece out of its top left corner.
The new zoom/focus gears (I got the 16-50mm and the 90mm one) are made out of hard plastic, rather than flexible rubber, so misalignment issues seem to be a thing of the past. They are also supported by freewheeling cogs on top left and bottom right (the driving cog is on the bottom left). On the downside, mounting the 90mm gear is very annoying - it has to be done just so, because if you push it into the housing for final alignment, it will push the lens focus ring forward, and force manual focus mode (if the ring is kept backwards, AF/MF can be chosen from camera menus, but forward position forces MF). I'll see how useful it actually is - thus far I don't see using it except in supermacro mode, to lock focus at minimal distance and focus on the subject by camera movement.
Moving my Leak Sentinel V5 XB was fairly trivial, but the UWT trigger gave me a surprise - the new housing uses a different reflector board that has wider-spaced mounting holes, which means that if I want to keep using it, I'll have to work with Pavel to get a new LED board. I'm not sure I'm willing to go to the effort and expense of it - my UWT trigger has been giving me issues anyway; in January it up and died in the middle of a liveaboard trip, and I finished the trip by using the pop-up flash on my a6300. I sent it to Pavel in Taiwan, and he replaced the hot shoe plug, which seemed to have revived it - except when I went on another trip, I found that it drains fresh CR1220 batteries within two dives. I got a SeaFrogs trigger with the housing, and so far I'm gonna keep using it - I hardly ever used TTL before, and I suppose I can live without HSS too. The SeaFrogs trigger is actually a tiny Xenon tube flash rather than an LED device, and by all accounts, it has terrible battery life, but I was surprised to see that it is able to sustain burst fire in continuous low mode (it started missing shots in continuous mid). I have ordered a small (60x60x15mm) powerbank and a low-profile right-angle micro-USB cable which should fit onto the trigger's charging socket - the housing has sufficient empty space below the camera to fit a powerbank up to approximately 75x70x18mm in size, so it should work, presuming that the powerbank will supply current on demand, without requiring a button press.
I will have to do something about the crossbar float arrangement that I've been running until now - I mounted a 60x200mm float arm on triple clamps between right tray handle and housing cold shoe, with the other clamp point holding strobe arm and focus light respectively, but now the cold shoe is in the center rather than left edge, so this is no longer viable. Best way forward, I think, is to get two very short (3") arm segments and mount them on triple clamps on both tray handles, facing up and in, then mount the crossbar float between them, and cold shoe ball adapter with a long clamp holding the focus light underneath it. This will give me the float capacity and a mounting point for my backup dive computer.
If I have the time, I'll try to take it diving this Saturday and see how it performs underwater.