Hi xyga here.
Created an account just to say I’ve been hoping for a similar feature, but for columns ! ^^
Reason: in x4 and x5 the kind of CRT imitation we get is a look similar to that of high-TVL like monitors, not looking like standard definition consumer tellys.
So one would say “why not output in x3 if you want that ?”, and I would agree but in most cases the issue is that the display’s built-in scaling – unlike in x5 1080p mode on my compatible monitor which is 1:1 – easily creates ugly artifact/patterns.
The only way to mitigate the issue is by tweaking ADC but it means making the picture way too dark.
Optimized modes also aren’t fit for this, so it’s draw only every other scanline while in generic modes that’s needed.
For me it is the only thing that’s missing on the original OSSC.
(Yep I’ve been bothering marqs a few times about it on shmups some time ago. ^^ )