these are arbitrary and an extremely stupid way to dictate what is expected of players around x skill level. The best way to do this would involve looking at the rough patternical levels at x skill level, and dictating what is regarded as "too difficult" for players at that skill level.
if anything, this should entirely be up to bn discretion for what constitutes as too difficult for a difficulty level, but hey.
Note snappings of consecutive 1/6 and above should not be used. This is to make sure beginner players start off with an easy experience in the game.
what is absurd about this, is that absolutely no time frame (or note frame) is dictated. A 1/6 in isolation is absolutely no harder than a 1/1 in isolation, or a 1/16th in isolation, or a 1/10000 in isolation; context is extremely important with regards to difficulty as, on their own, every note is equal in physical difficulty.
addendum: Consecutive implies that two consecutive 1/6's are too difficult for a given difficulty - two 1/6s on alternate hands will have no additional difficulty -- just like how two consecutive 1/100000000s
also have no additional difficulty. Using snaps to determine what can and can't be done in a chart is arbitrary and restrictive.
What is not accounted here, at all, is patterning. Even if you were to include a time-frame for difficulty (lets say, 10 notes) the difference between a 1/6 10 note 2h trill and a 1/6 10 note 1h trill is huge, and this rule has absolutely no dictation between the two. What you'd need to do for this rule to make any sense, is to gather data on all common patterns, and assess what BPM they are roughly playable by by a player at this skill level.
I would say, above anything, that common sense, and the dictation of the BNG should decide what is playable, roughly, for players at whatever skill level.
There is almost no way to list what is expected from players at any given skill level due to the huge variation in patterning that can be brought. 250bpm jumpstream for just 1 measure can range from, say, 7dan to luminal;
WITH NO SPECIFICITY TO PATTERNING, A RULE BASED ON WHAT SPEED IS EXPECTED FROM PLAYERS AT ANY GIVEN SKILL LEVEL IS, AT BEST, A SHOT IN THE DARK.
as such this rule should be removed; no specification on what snaps are or are not okay for players at any given skill level should be given, as, if anything, it would be almost entirely incorrect as it doesn't account for technical or physical difficulty. it is an arbitrary number - is 1/4 dense chordjacking okay when 1/6 streams are not? I believe almost everyone able to competently play would agree that a 1/6 stream is significantly easier than 1/4 dense chordjacking at the same bpm, yet this guideline dictates that the former is harder than the latter.
So, what should be done instead? Note that it is near-impossible (if not) to truly dictate what is capable by players at a given difficulty level. Even moreso, when the element dicating what is in which skill level is SR, which is absurdly flawed, and should not even be used as a metric for determining anything.
I suggest that, instead of providing objectivity in what BPM is playable, or not playable, by players at a given level (even with regards to patterns), you should explain the difficulty of patterning in the RC; explain concepts such as the difficulty of jacks, as they increase in length, they do not increase linearly but instead exponentially, and as such it should be understood that a chart utilising 2 note long jacks (minijacks) should not suddenly change into 3, or 4 note long jacks, as these are significantly more difficult, despite not being much of a change in patterning. Conveying this to charters reading RC will provide (atleast to some extent) a more competent understanding of the structure of patterning in comparison to other patterns at the same BPM.
Furthermore, explaining that 1H trills are more difficult than 2H trills, because 1H trilling increases in difficulty much faster than 2H trills (300bpm 2H trills are doable by most players at 9/10dan level; 300bpm 1H trills are beyond the peak of any top-tier player for any sustained period of time.) Would be significantly more useful than what is provided now. Then, a rough bpm (WITH LENIENCY) can be provided for each pattern, and then atleast, to some extent, a difficulty level acceptable for each difficulty can be determined.
As example:
Hard (As hard constitutes for 1st dan->4th dan)
Streams should be between 180bpm-230bpm, taking the length of a measure as baseline. Leniency should then be taken dependant on the length of the stream, longer streams increase the difficulty in stamina, so they should be slower for the same difficulty to apply (a 250 stream extended for a longer period of time would stretch into low/mid-insane) and vice versa. The same leniency should be applied to the technicality of patterns, the more technically challenging a pattern is, the slower it needs to be to exert the same overall difficulty, and vice versa. This leniency should be entirely down to the judgement of the bng.
With this; a basic understanding of difficulty can be presented in the RC.
(if you'd like more numbers for this, i can work them out roughly over the week, but you need to understand that SR is completely unusable to calculate the difficulty of patterns, and that hard-level chordjacks may rate a chart as insane, and extra-level longjacks may rate a chart as hard.)