Impossible? Nah, its possible

. It just requires the modder to take a abnormal amount of time of getting every little detail just right

. It can flow and not be stiff as a brick. Trust me, if you're that good at modding this game, many things are possible ;P. Things that I thought were impossible in the past eventually became possible.
I remember around 2-3 years ago, a jp modder showed me his long hair for HF. It resembled something like the above pics, but wasn't Kikyo really. It was just long hair that was not stiff as a brick

.
That was 2-3 years ago and that modder is gone and I do not have that file to show as a example nor a picture.
I was never really a "long hair" type of person (prefer short hair on my characters) so I rarely did long hair mods.
I am not particularly interested in doing this so maybe someone else can help you. Though I am planning to create a thread in the future with custom hairstyles/colors/faces so there may a long hair style in one of my posts. Just haven't had time to mod or make the thread though.