I didn't expect my CG gallery confession to be good But it's so nice to see that others want this too!!!
Good ideas are always random ones that just pop up. When I took it I was myself wondering something like " Yeaaaah.... why isn't that already in place"
Because I personally believe that it is actually a good feature for BOTH players AND PB. Having the gallery may give rise to our perfectionist tendencies and so some people are more likely to spend keys/diamonds to replay books/chapters just to get the art. It's good for the player because we get to admire the gorgeous at for more than just 10 seconds. It also helps the user feel even more rewarded when buying scenes.
How feasible could it be? Well based in my little programming experience I believe it might be moderately easy to do it. The only real difficult part could be the interface. So yeah, hopefully PB considers the gallery feature afterwards.