I think the next Macross songstress(es) that would lead in a Macross series would be somewhat like the ace of an idol or all-female-members group. From what I observed, the songstresses tend to be related with the current trend in Japan. Like Lynn Minmei was made during the Golden Age of idols in Japan. The Fire Bomber was made during the 90s where bands was the "in" thing then. These days, Japan has what they call "the Warring States era of Idols" (idol sengoku jidai), where idol groups or girl groups are everywhere. They may be in the mainstream market, underground groups (a lot of them are in Akihabara) or local idols (in a prefecture, district, city or town). That's why the morning Japanese drama 2 years ago, Amachan, was a big hit because it had that concept. Undeniably, AKB48 dominates the major charts whenever they release new material (as they just set a new record in Japan for having the most number of consecutive million sales of a single with their recent "Green Flash" single). Though I admit I can be wrong since I can't seem to pinpoint what was the trend when Sheryl+Ranka was made (I think anisong or moe was the "in" thing around 2008?).