A translation of the blog post by aakun on Everyday48 Forums is as follows:
The other day in a SDN48 Show, Captain Noro announced the above:Original blog post: http://ameblo.jp/sdn48official/entry-11048955915.html
since SDN48 was formed, 2 years and 2 months have passed and ever since the beginning,
we have always received warm messages and support from the fans.
we would like to use this chance, and thank the fans one again.
For all the SDN48 Members to follow our different paths we aim in this life
all the members together decided to graduate from SDN48
With all the current members in a Goodbye Concert to be realized in 2012/3/31, we will finish our first chapter as SDN48.
for all the members to make our individual dreams come true
we will begin a journey to a new stage.
from now on too, just like always until now, please keep supporting us.
This is definitely sudden and unexpected. SDN48, while not as popular as its sister groups, has been doing reasonably well. As such, many were caught off-guard. I do not know of any rumours or other reasons for this mass graduation to happen, so for now it would be best to take their word for it and that the members have decided they wanted to do something else.
I am still in shock. It was not too long ago that I watched SDN48 live in Singapore and there were no hints of what was to come. Had the girls decided then and put on a fantastic show anyway, or had they not decided anything? This is a huge decision and I would think it had been decided for weeks at least. Yet, I still remember Ito Mana prompting the audience to visit the theater in Akihabara in future. It certainly didn't seem like they were thinking of graduating. I'm also angered because I believe this is in part thanks to creator Akimoto Yasushi neglecting the group in general and the girls may have felt there wasn't any way to develop further.
Lastly, obviously, I am sad because I love SDN48 and I thought they were the best thing to come of the 48 franchise. I'm really reluctant to see them go. Though SDN48 may not be disbanding per se (adding members after all current members are gone is a possibility), I don't think it'll be the same without any of the current members.