On live dan calculators
Dans are extremely subjective, there are way too many different systems, they are exclusive to a single keymode and don't work well with any LN percentages outside the very narrow ranges of rice/LN dans.
So how about instead of trying to create a program that somehow approximates this already imperfect difficulty we just make one that just shows several values from actual rhythm game systems. We have MSD, sunny rework star rating, Quaver and Interlude ratings, all with their strengths and drawbacks, a program that would tell you all 4 of those at the same time would give you much more useful info than some very approximate dan rating, and it would be easy to fine tune since you can just pop the map into the respective games to see how close the program is to the real values.