I really don't think covered reverse arrows should become diff-specific. This heavily implies that it should be "okay" for higher difficulties. It should not. Covering repeat arrows in a way that makes them unreadable is an unfair gameplay mechanic.
I'd rather have this rule further clarified because a lot of cases of "covered repeat arrows" are actually fine, such as slider-head overlaps (which won't be obstructed by combo-burst) or slider-body overlaps (there's often enough visibility). It's mainly tail/repeat overlaps and overlaps with very little room in between slider/repeat arrow.
@quanhitter39: Just want to clarify: why "covered reverse arrow" is an "unfair gameplay mechanic" imo is because it's not a mechanic you can read/sightread. There is zero way of reading and expecting the repeat arrow because the only way you can tell if a slider is a repeat is if there is a repeat arrow, and if you can't see the repeat arrow, there's literally no other indicator. You would play the slider with the expectation that it is not a repeat. This is why it becomes an unfair gameplay element.
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Possible ways of clarifying cases where covered repeat arrows should be unrankable, with diff-specific guideline in mind:
-Repeat arrows must be visible for at least 1/x a beat before they are meant to be played. (4/1 for E/N, 2/1 for H, 1/1 for I/X?) <--- Bearing in mind 1/1 at 180 bpm is approximately 350ms which is higher than AR 10 already.
-Repeat arrows must be visible for at least 3/4th's the AR of the difficulty. (would be more general)
Cases where the repeat arrow is obstructed by a slider-body should be considered case by case though, I can see some slider shapes being fine (linear/curved, simple shapes) while others with very complex designs potentially obstructing the location of the repeat arrow because of maybe the slider-ball covering the area the repeat arrow is supposed to appear.