I guess none of us are really surprised, considering Karin already had a solo tour. Good for her.
I'm looking forward to what Juice=Juice will be without her. Especially until 2nd gen was added J=J was the Miyamoto Karin show, they've toned it down after that, but she was still very obviously the ace. However, other girls like Tomoko, Sayuki and Ruru definitely stepped up their game.
J=J's new single will be released in April. Karin will start her solo performances in fall. I guess she'll take a few months to train a bit, like Airi did.