Considering that ayaka easily attracts casual listeners, I'd say she has good chances of reaching 1 million and her charting power when it comes to albums is amazing.
As for arashi, well I'd say they will sell over 1 million, but it's hard to be sure, I guess All the BEST will show how popular they are in fact. The fact that their previous compilations sold less than some of their studio albums tells a lot. But we'll see.
I'd say I agree with Ryo on this one