I think I may switch to horde a few months before expansion just so I can switch back to be worgen when it hits. Assuming that they don't add the ability to switch races
if youre talking about the Faction change thing. You can only switch back to your previous race, you cant do like Nelf > Tauren > back to alliance as worgen.
They mentioned the ability to switch races at Blizzcon coming shortly after switching factions. Read it on MMO, don't have an actual blue post to link at the moment.