Airs Wed (3rd week every month) on NHK-BS Premium @ 20:00-20:59
It was announced some weeks earlier that Kokubun Taichi would be stepping down as the MC of Shounen Club Premium, but at the time, it was unknown who would replace him. However, as revealed by today's (3/12 JST) issue of TVstation (1, 2), KAT-TUN will take over and become the new MCs. Their first episode will air 2014.04.16. (As a side-note, Taichi's last episode airs on 2014.03.19. KT is listed as one of the guests along with other Johnny's talent.)
Other details have yet to be announced, so it's unclear if the format of the show will change and how KT will host (as a group? paired off? etc). Further info will be added when available.
In the meantime - congrats, KAT-TUN!