Thanks to each of you for your persistence.
Here is the most recent update from David Chatham:
The Upgrade Process has slowed and is not making reasonable progress. Within the last hour, a roll-back procedure was started also on another server, so that one way or another we can get students and faculty back into their courses by tomorrow morning. Probably, the roll-back will occur before that, but estimating so far has been off the mark.
Since both the planned update and the emergency roll-back will be proceeding at the same time, there is a small chance that the Update will still succeed, but if not, the roll-back will allow users to re-enter their courses. The roll-back will not have the benefits that we were looking to have with the update.