Standard maps aren't made in the mindset to be challenging, worthwhile, or played in taiko, except for the handful of taikosu! maps. They are made to be played in Standard. Not to mention most standard conversions are considered unrankable because of SV and finisher usage. So they don't even fit with the criteria a taiko map should have. Essentially, they are a completely different style of play from what the community considers taiko gameplay. (as shown from the long discussion of making the taiko ranking criteria.)
So, there is no reason they should be included in the taiko ranking system.
Anyways on terms of mod scaling, DT is obviously the hardest mod. Not just because of speed, but because it adds more OD to the map as well. In my opinion HR and HD are equal. HR provides slight vision impairment from higher speeds, and a big boost in the OD. While HD provides a substantially greater vision impairment that can severely effect your accuracy, even though there is no OD boost. This is based off a theoretical player who hasn't played either mod enough to get used to the differences these mods make. We all know after a while these mods become second hand.
I can't really say anything about FL because there hasn't been a breakthrough in how to play it efficiently without having a good memory or playing the song a million times to memorize it. Something that doesn't equate to raw skill in my mind.
As far as note density goes: I would like to think a ratio of notes to song length would be accurate, but every song is different and just isn't possible without over/undermapping. So basing it off something like BPM would be more accurate, in theory.
So, there is no reason they should be included in the taiko ranking system.
Anyways on terms of mod scaling, DT is obviously the hardest mod. Not just because of speed, but because it adds more OD to the map as well. In my opinion HR and HD are equal. HR provides slight vision impairment from higher speeds, and a big boost in the OD. While HD provides a substantially greater vision impairment that can severely effect your accuracy, even though there is no OD boost. This is based off a theoretical player who hasn't played either mod enough to get used to the differences these mods make. We all know after a while these mods become second hand.
I can't really say anything about FL because there hasn't been a breakthrough in how to play it efficiently without having a good memory or playing the song a million times to memorize it. Something that doesn't equate to raw skill in my mind.
As far as note density goes: I would like to think a ratio of notes to song length would be accurate, but every song is different and just isn't possible without over/undermapping. So basing it off something like BPM would be more accurate, in theory.