I finally got my score back to 99 yesterday after losing 2 points last week for a single collision warning.
I think the problem is that too many people have gotten their scores back up to 99 now, while Tesla still wants to limit the rollout. It's because people aren't driving normally while they are observing their safety score; they're gaming the system (by driving extra miles along "safe routes" they don't usually take), or rebooting the computer after a collision warning, etc. So the safety score alone is no longer a reliable indicator of risk. It doesn't indicate how safely people drive, it indicates how effectively they play the "game."
For each point the threshold is lowered, the duration will increase. I seriously doubt 10.3 is actually coming to cars with 99/100; it might be version 10.4 or 10.5 that finally comes to cars with 99, and not until November. Then cars with 98 will get it another 3-4 months beyond that, or the rollout might pause for an undetermined amount of time, or some other factor will be introduced along with safety score in order to restrict the rollout.