I can definitely see these cover illustrations as having been recently done with the idea of using them to promote the ice show.
But Usagi's holding roses, which makes me think of the cover illustration for the art book that was announced in 2017 where all the girls are holding roses, so possibly these illustrations were done way back then? And they've been working on this since around then? Perhaps the art books have been delayed because they wanted to include these covers and thus wait until the color editions could be released?
Whatever the case, I can't wait to get these! I hope fans outside of Japan will be able to get (DRM-free) copies. Only 3 more days!!!!!
ETA: It seems the coloring has been edited a bit from the original 2014 Roppongi Hills exhibition showing:
Seems like they've removed some background colors and changed some text colors, which would make sense for a print release to cut down on ink costs, but for a digital release??