I believe the (over) reaction to freeze everything is due to grade changes that occurred due to SUM being overwritten and reused as Natural instead of creating a new aggregation method.
During all phases of the discussion on Natural Weighting, there were suggestions for implementing it as a new aggregation method. When that suggestion was first not understood, then ignored, promises were made to ensure no grades would be changed during the upgrade process. Maintaining the integrity of grades would be a priority.
This was clearly not what transpired.
First, people used SUM incorrectly and counted on bugs.
Second, developers fixed those bugs without regard for grade integrity.
Natural weighting should have been implemented as a new aggregation method. This would have allowed people to adopt it in their own time. As this was not the case, there seems to be a fundamental disagreement on how to handle things like this in the future.
I'm with Tim on this, don't throw the baby out with the bathwater. We're making this too complicated. If we take care not to make mistakes for the sake of getting things done quicker, we won't have these problems in the future.