Not sure how big of a lag you're talking about, but I remember the website for the expansion has usually gone up during the announcement (usually during the trailer or slightly before it) and there's almost always been more information than the trailer gave away.
So, for those unable to watch the stream live, refreshing https://worldofwarcraft.com/en-us/dragonflight or https://dragonflight.blizzard.com might also be a good idea.