At this point, though, the Dark One needs to be provided with a body capable of channeling that meets other criteria we are not 100% privy to.

It seems almost like it is more likely for every Forsaken to be transmigrated now since there are so few capable characters to replace them. During the Age of Legends, it was more likely that many capable Forsaken could take the place of those who had fallen in the higher levels. All they have now as possible replacements are Mazrim Taim, random Black Ajah Sisters and darkfriend Ashaman. Basically it is more important to preserve as many of the 13 as possible because there is such a lack of possible replacements.