One thing that hasn't been mentioned much, unless I missed it upthread, is that the A7II is heavier than the original A7. 556g as opposed to 416g from the specs I've seen.
That's not a massive amount in itself, but if a light camera is one of the reasons one chose to go mirrorless, it all adds up. So, from that point of view, it's not about the $400.
That aside, I never shoot longer than 50mm lenses, so IS technology is of little use to me. Even at low light (and 75% of my work is hand-held night photography), I very rarely shoot at higher ISO than 3200 (even at 6400, the files are clean enough), which gives a plenty fast enough shutter speed. Faster autofocus? Can't knock that. But I can't actually remember ever having any issues with focus. If I need fast focus, then I break out the dSLR.
The ergonomics do look better, though. I do remember, when I first got the A7, finding that my finger wanted to go where the new shutter button will be. That said, it does make the new camera more bulky. Another reason why I'm happier with the original A7 for now.
If they had removed the low pass filter, kept the weight the same, got rid of that daft RAW compression nonsense (not that it's much of a practical issue), perhaps even improved dynamic range, then it might be more tempting.