I believe that they (USM, the management office of Dai, Shizuka, Kanako and Kana) started working on this project soon after Hyoen 2019 was finished just like they started on Hyoen 2019 as soon as Hyoen 2017 was finished, and booked Yokohama Arena. They might have initially planned a show as complex as Hyoen 2019, but decided to make a less complex revue-type show instead because their production time would be limited with Dai being in Florida with Kana training for ice dance and this COVID-19 pandemic.It sure sounds and looks intriguing. But this is extremely surprising and very short notice. It was probably planned for a while, but put on hold due to the pandemic? Hopefully they can run the shows safely (on the bottom of the website it says that masks are mandatory and that there will be temperature checks; additionally I hope they won't sell the max. capacity of seats to allow for enough distance between audience members).
I hope there will be a livestream because many people living outside big cities are still reluctant to travel.