Thanks to extensive performance work before and after launch we were able to start with a cap of 4.000 and increase it rapidly to where we are now - 7.000. At this point, performance can vary heavily with just 500 players difference. We have optimized our code to a point where it is very hard to make any further improvements without a complete rewrite or an improved version of load balancing. Not only that, it is also a question of design.
In theory a server with 10.000 players online at the same time sounds great, but in practice? Quest and daily hubs would be overfarmed, Dalaran would at some point probably become unplayable, and several other issues would definitely show. Instead, it may be better to open a second realm if we see that enough players would be interested. That means definitely more than 600+ we saw in queue on sunday.
Nonetheless we continue to work on performance for several reasons and will soon be testing another patch on live that has the potential to let us raise the cap once again, possibly up to 8.000.

