I think they'll do RAF for expansion, it means a LOT of new sales/accounts for them. Think how many people want to level up new races, but want the RAF speed, and they'll shell out the money for Classic + BC + WOTLK + Cat + a new account just to get the RAF bonus vs just buying Cat.

I think they said they might make the "realm first" goblin etc... to be leveled without RAF and Heirloom items though.