Kansai TV who's producing the drama says the work will be of the mysterious type.
There's one more thing. In the profile of Nakayama that was printed along with the article, it says that he will be part of a Johnny's Jrs concert that will be held at Tokyo International Forum (東京国際フォーラム) on June 7th.
Does anyone know anything about this? Juniors Fanclub I'm pretty sure didn't receive this news yet, and it's uncertain if it's for all Juniors or just Kansai Jrs. Then again, if it's Tokyo International Forum, it should be Kantou and Kansai Jrs? No official information from the jimusho, but considering it's Sports Hochi and not some rumour/tabloid, you can say it might be true?
Source (Sports Hochi)
Edit: Sanspo | Daily Sports
According to Daily Sports, Nakayama has been doing concerts around Kansai, and that it'll be his first time to do a concert in Tokyo, so it sounds like it's a Kansai Jr concert, but held in Tokyo.