Regarding Taylor, her popularity has been on a downward trend since fearless, and will continue to decrease because as she gets older she will lose her appeal to the millions of American children who love her so much. I predict 3.5 million in US sales for her upcoming album, and 2 million for the one after that.
My prediction threads:
Wii U will sell under 40m units (made on 14th September 2012)
PS Vita will sell under 20m units (made on 30th September 2012)
Wii U will sell under 7m in 2013 - I was right