This would feel much more intuitive to me:
1 2 3 4 ^
5 6 7 8 v
(scrolling vertically)
I see the point, and it's definitely a good point, but let me do a bit of history here... attached is a screenshot of an early version (never published) of my Attract Mode layout. The scrolling and arrangement was as you suggest, the first iteration had a very simple grid layout where tiles would just change with no scrolling whatsoever, the second one (the one in the picture) used the conveyor module to have a decent scrolling. Then I saw Oomek work on Silky theme, Ambiance HD and the carrier.nut module, and decided I wanted something different, smoother, more "modern looking".
Arcadeflow was born adapting the look of Plex Media Player and the look of a mockup someone made on Hyperspin forums, both these had horizontal scrolling tile rows. There are two reasons why it works better in horizontal than in vertical: aesthetically I wanted a very clean look, and vertical scrolling would've interfered with the title block (which is actually opaque in the first mockups with tiles sliding behind). Also there's a technical reason: to be smooth carrier module needs to pre-load some pictures outside of the screen, and update them accordingly. With two rows, I add some out of screen columns to the left and right, and things are pretty snappy. Scrolling vertically with 4 or 5 tiles per row means that to have three rows out of screen I'll have to add 4 (or 5) x 3 = 12 (or 15!) tiles per side (top and bottom) which can be a bit overkill on many systems (including my poor macbook pro
)
In the end, who knows what future will bring? In the past I've said many times I was not going to implement something, and actually changed my mind a week later
But changing Arcadeflow to incorporate vertical scrolling would be a very large overhaul of the whole layout which I don't whink will happen so soon...