I thought this unit might be one of Kago's random, impulsive, grab an opportunity when it arises ideas, but 2ch found a quote from her blog last year where, in response to a question about what her dream was, Kago said something like "Honestly, I want to create a unit and sing! lol " so at least she has been planning it for a while. She probably feels like she has some unfinished business left in the idol world.
Also, she has enough shoes to outfit an AKB48 size unit