I understand the desire to disable the preview feature, but the fact that this hasn't already been implement suggests to me that it's a bigger burden on Jon's half than simply flipping a switch. My guess is it's tightly entangled in other features. For example, the GoTo File. How should the goto file degrade (without having the instant previews as you search)? Should preview only be disable for clicks in the sidebar? Then more problems arise...
I may be completely off base though. Maybe Jon secretly has a switch called "Disable Preview" that he's just not sharing
But if I am right and disabling the preview is too big of a hassle, I think improving it both functionally and visually with eliminate the headaches.
But I'm sure Jon's well aware of all of this (I guarantee he's seen all of the posts you've linked to) and he's bound to surprise us with what's to come