I hope this actually happens. I would definitely play. Seems like it's still a ways off. I agree that it would be better to resemble HBD and not HD or GD. Although even further down the line, maybe a college hockey sim would be okay, if there were enough interest.
As for beginning on certain days, I think it would work like HBD, where the world would start whenever it filled up. There would probably not be Sim AI teams like in GD and HD.
Maybe they will take a lesson learned from HBD, and not allow too many worlds to open at the outset. This will avoid a problem that HBD encountered, with too many worlds and not enough users.
I expect this won't be coming any time soon, but I hope it does eventually!