Pro: Good idea, a "We're full and Closed" sign is better than a "We're full and Closed, but 15 people got lucky and you didn't".
Con: But now how am I going to estimate my wait or guage when a good time to refresh the server list might be if say I'm waiting to get into a capped arena, not knowing if it's at 101/100 or 154/100?...
This concerns me as it may be a source of generating additional frustration against the CAP system rather than intending to lessen it.