I just realized that I never talked about the reason I didn’t do a 3DS.
The way it is now, HSMs shader doesn’t work with dual screens that are different aspect ratios, like the 3DS. I think that eventually it will work with side-by-side screens, (Since that would only require moving the center bezel a bit.) but I’m not sure how it would handle Top-bottom setups, since it would require different bezel widths for each screen.
So for now it is one system that won’t be on my list.
If you’d like to use an overlay for now I have a passable one in my “Misc-Overlays-Borders-Bezels” repo in the “overlays” folder.