See, it's been used properly before, that's the thing. It doesn't make sense as a rule because it clearly can work well. It's more fitting as a guideline / removed.
The whole point of guidelines is to encourage / discourage certain mapping behavior, but allow cases where it is handled properly / carefully.
In the case of sliderslides, if a mapper doesn't know what they're doing, it'll be really obvious when the audio starts popping like crazy.
If they do know what they're doing, you'll get stuff like fanzhen's map. They shouldn't be stopped just because others might not do it right.
See, changing sliderslides causes really obvious and nasty audio pops when done incorrectly.
This sort of thing has shown up in sets before, namely https://osu.ppy.sh/b/722224 , where a slider was changing sliderslides to match the piano.
The audio popping was so bad that it got removed and is not present in the ranked version.
It wasn't removed because of rules, but because it clearly wasn't any good. Modding took care of it, no problem.
For an example of how these can be done without audio popping, I've prepared an example osz.
http://puu.sh/lO7bV/5719bc29b3.osz
This goes through 5 different sounds on the same slider.
When played with NoMod, Half Time, or DoubleTime, there is no audio popping whatsoever due to how the files and inheriting sections are set up.
The only audio popping noticeable is in the editor and when NoMod is watched at 2x speed (neither of which are gameplay).
Really, the only time a mapper would want to do this is if hitsounding sliderticks just isn't cutting it, or if increasing slider tick rate is causing gameplay issues.
No reason to stop them from even attempting it, though. If it comes out bad they'll learn from their mistakes and fix it / try something else.
If it comes out good, why stop them?
tl;dr No need for rule, it can be done properly and it's obvious when it's done poorly.
If you want to discourage its use, put the rule into guidelines. That way modders will point it out more frequently, too.
The whole point of guidelines is to encourage / discourage certain mapping behavior, but allow cases where it is handled properly / carefully.
In the case of sliderslides, if a mapper doesn't know what they're doing, it'll be really obvious when the audio starts popping like crazy.
If they do know what they're doing, you'll get stuff like fanzhen's map. They shouldn't be stopped just because others might not do it right.
See, changing sliderslides causes really obvious and nasty audio pops when done incorrectly.
This sort of thing has shown up in sets before, namely https://osu.ppy.sh/b/722224 , where a slider was changing sliderslides to match the piano.
The audio popping was so bad that it got removed and is not present in the ranked version.
It wasn't removed because of rules, but because it clearly wasn't any good. Modding took care of it, no problem.
For an example of how these can be done without audio popping, I've prepared an example osz.
http://puu.sh/lO7bV/5719bc29b3.osz
This goes through 5 different sounds on the same slider.
When played with NoMod, Half Time, or DoubleTime, there is no audio popping whatsoever due to how the files and inheriting sections are set up.
The only audio popping noticeable is in the editor and when NoMod is watched at 2x speed (neither of which are gameplay).
Really, the only time a mapper would want to do this is if hitsounding sliderticks just isn't cutting it, or if increasing slider tick rate is causing gameplay issues.
No reason to stop them from even attempting it, though. If it comes out bad they'll learn from their mistakes and fix it / try something else.
If it comes out good, why stop them?
tl;dr No need for rule, it can be done properly and it's obvious when it's done poorly.
If you want to discourage its use, put the rule into guidelines. That way modders will point it out more frequently, too.