So, these two achievements are very interesting in their wording.
# Realm First! Level 85 Lost Isles Goblin - First goblin on the realm to achieve level 85 who completed the Lost Isles quest chain.
# Realm First! Level 85 Gilnean Worgen - First worgen on the realm to achieve level 85 who completed the Gilneas quest chain.
Notice the "who completed the Lost Isles/Gilneas quest chain" part. I believe it's safe to assume that we will be able to race change to the new races upon Cataclysm's release based on that. I, for one, am relieved and excited more than ever now.