I did some test mods in the layout.nut, but I used Yaron's theme for that since it had the side bezel support already (so I don't even know which post is more relevant for this discussion). I "squished" the bezels at run time so they are displayed narrower, and placed the left/right sides of that separately. I actually think it looks pretty nice, as it keeps the full screen snapshot while also showing the full bezel (albeit squished). The main issue I ran into is that the snaps have varying aspect ratios, and similarly the visible bezel widths differ from game to game. Nothing about the bezel files tell us the inner width, so I had to take a guess on a percentage that looks good on most games.
Then as an experiment I tried enabling it for horizontal games as well, and it actually didn't look too bad. Mainly because the bezels for those games are already much thinner than the vertical game bezels. Could be enabled as a separate option perhaps. But to handle it better, we'd probably need to compute the aspect ratio for those horizontal snaps, and if it is too wide (basically consuming the entire available area, as some of them do, we could shrink the snap size a little).
Here's an example of a vertical game (1943) and a horizontal game (Defender), with the bezels squished to 65% of their full size. I can share the code I used, but it was based on the "At-The-Arcade Multi-Cab" layout so not directly applicable for this layout.