Keep in mind that in the current CL group stage, each team plays six games. In the new format, each team would play 10 games and the sides finishing between 9th and 24th would play another two in the playoff round. That's literally twice as many games. It will be incredibly hard to fit it into the calendar, and almost impossible to guarantee two-week breaks between games. Unless UEFA are willing to keep it going throughout December and January as well, which, again is a potential logistical problem for a lot of the continent.