What it means is that coach is completely sold out and there are at least 4 open seats in First. Could be more than 4. Right now there are no F seats available so no one will get an "Elite upgrade". F seats are gradually released if not sold for revenue.

Chances for Silver depend on the number of Golds and Plats that were not upgraded yet as there are no F seats available.

Look in another thread discussed today on this board about the check-in process and it's effect on upgrading.