As of now since there is still no confirmation about this, this news remains to be a rumor until we hear something from the agencies of the actors whose names are mentioned here.
So far, I don't think we'll be hearing anything concrete on this from KeyEast as Kim Hyun Joong is still busy with Mischievous Kiss. On the other hand, Kim Jae Joong is said to be in a 20 episode long drama, Poseidon which Kang Ji Hwan will be starring in. This drama is said to start shooting this September and is set to air in the early half of next year. As for Jung Yong Hwa, after being rumored to be in Mischievous Kiss to play the lead role, we still have to read about his next drama. But currently he's busy with CNBlue and We Go Married.
Anyway, to read more about this rumored drama, read Ode's translation of the article posted on her blog. Much thanks!
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[Article] Cinderella
source : shizuoka daily news ++ blog.daum.net/elley0606/289
Korean to English translation by Ode / SS501ode/blogspot.com

On the 10th, an explanatory (?) conference was held at the HAMANAKO LAKESIDE PLAZA in Hamamatsu, Magna-resort for upcoming new Korea-Japan collaboration drama work.
Representatives from the production company M-Media gathered together to release the outlines of the drama.
The drama is titled "Cinderella", and it is expected to have a total of 20 episodes. The script is unfinished as of now, and there is also a need to find possible collaborations and investors.
Shooting for about 2 episodes will begin in Japan beginning next Spring onwards for about a month.
And is targeted to be broadcasted next May in Korea, and will also air in Japan. Staff, PDs and casts will be the top ones in Korea; the PD will be Pyo Minsoo PD nim who has personally created many aplenty of Korean dramas.
Though it's still undecided as of now, the female casts are short-listed to be Song Hyegyo, Kim ah-joong, Yoon Eunhye etc. While male casts are short-listed to be Kim Hyunjoong, Nickhun, Jung Yonghwa etc.
Local residents of the country will also be invited to appear as extras.