Last week's "Flyertalk 1" tour of ORD was very illuminating in this respect. During our tour of the Ops Center, we spoke with the guy who was actually responsible for updating the arrival/departure times of flights. In short, the process is manual. We saw a computer screen of flights and gates, where planes are supposed to be and when. When everything goes right, there's nothing for him to do...which is never. As soon as delays, even small ones, begin, the ripple effects have to be taken into account. This flight has a 10 minute ATC delay, which means the flight supposed to come in after it has to be given a different gate...but which one? Another plane has a mechanical delay, but there's no firm answer on how long, and in the meantime "the guy" is trying to shuffle around three other planes into optimal gates. So the mx plane sits at the gate past its departure time, and people grumble. But The Guy has bigger fish to fry, and in any case doesn't want to update the time until he knows something relatively firm. And then a delayed 747 comes in with loads of 1Ks to accommodate...how best to do this? And everything else gets put aside for a few minutes...
The point is that the system is "automatic" only insofar as it takes information that is provided by a human and propogates it throughout the various subsystems. I had always assumed this was completely automatic, but it's not, and to that extent there will always be lags and mistakes.
So, back to the OP, there's really no point IMO to sending an EasyUpdate message that boarding has begun. If everything is on schedule, you don't need it. If everything is not -- and the only way to know this is through the same human-guided systems described above -- then again, the only and best information you can have is the same EasyUpdate message announcing a delay. (FWIW, we were told that monitors at the airport and EU messages come from the same source...which has a 5 minutes or so delay from the instant a change is effected in the Ops Center.) In any case, as we all know, the EU system barely works under normal conditions. Adding several tens of thousands of additional messages a day certainly wouldn't improve its efficiency, right?