The one thing I heard was that they wanted to start the season Dec 1 so that the Finals wouldn't conflict with the Olympics in Japan, which the international players want to play for. I can see the logic there, but still, they could conceivably play Game 7 of the NBA Finals in the 2nd week of October, and then have to prepare for training camp like 3-4 weeks later. Yes it will only apply to the two teams in the Finals, but even the Raptors got 3-4 months off after winning the title last year. It's a grind. This playoff schedule will have no travel, but also less time off in between games, after they will have already been off for 3 months quarantining. If the Olympics is the reason, then I could see it staying on December 1, but a lot of players are going to hate it.
And yeah, I think this will be a permanent change for the NBA. Without the Olympics, they might start the 2021-22 season on Christmas Day, which is what I thought they'd do this year, but either way, it's better for them to avoid the NFL as much as possible, and a December start date does that.