They had been making it seem like Meiko was important because of her anniversary (having her speaking at Miku Symphony and next to Miku for Pocari Sweat), but that's long gone now. I think by the time Miku is done, it could be anyone's chance. Note for those who haven't heard, ALL of the Cryptonloids had been being worked on equally throughout this entire 2-ish years (not counting Miku). We've only heard the new voices for the Kagamines in the Project Sekai clips, so we've actually heard more Meiko than anyone other than Miku so far.
Anyway, I honestly hope it's someone whose voice bank is older (as in Kaito or Meiko). I am getting really sick of waiting for Kaito, been waiting to buy him for as long as this thread is old...
We mentioned this on Discord, but do you think they will sell Len and Rin separately? If Miku has 3 voices and everyone else does, too, then what's the point in selling them together? It's also already firmly established they are a pair, but I think they don't necessarily need the gimmick anymore because they have fans now who might not want to buy both of them.