WotLK New core update and arena teams

[rix]

So after reading the devlog, I'm not 100% clear about the core update. Are the realms going to merge on the date of update or will the core be applied on that day and the merge after? What will happen to arena teams during the merge?

[Sixtyninee]

The merge will obviously take place after the upgrade, as it says Ragnaros will be upgraded (at some point) afterwards.