I'm surprised there aren't more entries already, but I guess it's early yet.
This is the kind of state of where I'm at for the moment:
I'm experiementing with setting up some nice semi-opaque windows for text & quotes on the back cover, rough sample of what I'm talking about here:
For other 2+2 texts there's been a tendency to just plop words down over a plain background, which is usually easy. It's not a good idea here because there are some legibility concerns due to the textured background. Problem is if I create a window I'm definining the space where the text has to go... I'd rather make the window to fit around the text rather than have someone else try to fit their text in the window...
The spine by itself, based on a 1 inch width:
Still very rough but all of the comments are helping me steer this thing