I know this theme is essentially mame-exclusive with regards to how it displays and handles data, but I was wondering if there was any way to force the aspect ratio of the game snaps to be horizontal.
You are right, Arcadeflow is heavily tied to using Mame or arcades, and especially to use screenshots as artwork. The idea behind this theme was exactly to build some nice graphics for machine that don't have proper "box art" (flyers are nice but sometimes a bit messy and difficult to find).
Building an entirely new "Consoleflow" theme would be interesting: consoles have some advantages like proper box art (should just tweak the drop shadows to be dynamically generated and not "faked" like they are now
), screens are always horizontal, probably no need to use "logo" artwork in the grid layout etc. I'll think of it but I'm not so much into console emulation
To answer your question more directly, I can fix something on the fly to force Arcadeflow to always display horizontal aspect ratio tiles in the grid, but the theme will force the artwork to fit in an horizontal 4:3 box, so some stretching of box art might occur. What is the aspect of SNES boxes?
[EDIT] Have you tried previous versions of Arcadeflow? Up to 3.7 (I think) it used actual snap resolution to detect horizontal or vertical games and should work with box art too...