There is still hope for solo artists! it seems that AKB's peak is over
Talking about yearly sales, also other 48 groups have also ended their peak (Apparently)
SKE48
http://asianumbers.galeon.com/ske48.html
NMB48
http://asianumbers.galeon.com/nmb48.html
And recently debuted group HKT48 has got really low sales (200k) compared to the other 48 groups (400-600k) so maybe it's their last 48 group (at least on Japan..)