I don't know if it was mentioned anywhere yet, but I'll just post it here again in case someone else missed it.
Tsunku wrote on his blog that he was surprised.
That does NOT mean he didn't know about this announcement. What he refers to is that he was surprised at the girls' (Ayaka, Kanon) growth that showed when they suggested the addition of member to the staff. Hearing about that, made him surprised.
There's no way he would find out about it through Hello!Station.
I don't know if someone thought that or not, but just to clarify for those who don't understand/read Japanese. Before any mistranslations and/or wrong assumptions starts showing up.
I personally think that it's about time, too. In the announcement Ayaka and Kanon mention it several times, and it's even written on the video that the 2ki members have been vocally worried over what would happen to S/mileage once Ayaka and Kanon leave. More members is exactly what they need to get the confidence and motivation they/some of them lack.