Wasn't the Pandaren race some sort of joke originally? I thought it was April 1 or something when I heard about the new WoW expansion, but alas, no. I recall there being the Brewmaster in WC3, with what seemed at the time some half joking lore behind it.
Did the premise for this whole expansion just come out of nowhere or has it been building since then?
Best Answer
The Pandaren race has been around since Warcraft 3/Frozen Throne times when a monk named Chen Stormstout helped out Rexxar in an extra campaign (as you mentioned).
In regards to the April 1st joke, it was a joke back in the day. The information can be found here: http://www.wowwiki.com/Pandaren_Xpress
As far as the building aspect, there has been a lot of talk in the background about the race being added in going as far back as the announcement of the last expansion (Cataclysm). Most thought that it would have come in Cataclysm instead of the Goblin or Worgen, but that was not the case.
More info about the race can be found here without too much copy/pasting: http://www.wowwiki.com/Pandaren