there are a few different types of raiding guilds out there. first one is the hardcore guilds who will be looking to push hard and enter Kara/Gruul's Lair/Magtheridon's Lair in the first week. then there is basically everyone else who will take a more relaxed approach and look to enter those raids weeks 2-4.
Anyone in the hardcore guilds who was re-rolling to a BElf or SpaceGoat either put the time in to get to 60 before expansion hit or, if they didn't, would've been boosted by people in their guild to speed level.
Everyone else, it doesn't matter - if guilds want the advantages of having Blood Elves or Draenei in their raid then they will wait - not every guild is wanting to push for world first/realm first or whatever.
As other people have said; Blood Elves and Draenei weren't in the original game until the actual launch - we got them in prepatch. Guilds waited for them to level back then, and they will now (or they will help speedlevel them)