read the websites and lore people NOT bull shit it is CONFIRMED from INSIDE sources that WON'T be revealed because they would be lost...
read over the multiple posts on lore of goblins and worgen it is mostly true. but what they missed is that goblins are not as a whole an empire, the majority of goblins are split between the steamwheedle and Venture co. factions whom are fighting among eachother for resources.
that still lieave 2-3 trade princes, one of which allied himself to hte horde when he belived they had a chance during the second war. a CHANCE in the second war as split up settlments. they are now a fully blown empire, its easily viewable that they would go straight for horde now that the chances of them succeding are so greatly increased.
but then we are left with the worgen, now contray to popular belief there are more then one kind of worgen, and they are not werewolves. there are four known clans the Nightbane of duskwood (alter dimensional) there are the Moonrage (cursed my Argual) terrowulf (alter dimensional) and finally the Wolfcult(yet agian cursed vilalgers thansk to argual, this time under the command of the lich king)
now we know from lore that the alter dimensional worgen did originaly claim to help Velinde star song, yet they used her to summon more of themselves from another dimension. when she went to find argual for help she disapeared (belived to be in the other dimension now) this COULD lead to a plot where the worgen break from the other dimension where she has befrended them fully and now brings them back to azeroth as an ally to the alliance.
then the other possibility (more likley) is that the residents of gilneas who live only slightly south of the Moonrage worgen were to be inflicted with the curse themselves. and have taken a liking toward staying that way (if this is true the new strenght from such a evolution would be a good explanation for Gilneas survivng the scourge and possibly even the naga) these Gilneas Worgen could easily fit into lore to be allined with the alliance.
and maelstrom it wasnt a big guess the game goes in orgder of weak to stronger lore wise, the black draon flight and black rock orcs where no match for the might of the Burning legion, who where defeated by Illidan, whom was defeated by arthas, who is no match for the source of all Azerothian universes evil, Sargeras, who's avatar lays entombed in the maelstrom.
so to finish this it aint totally it aint totally impossible. its very real all in all.
and regarding death knights, it is possible goblins COULD have become them during WOTLK, but the rule of the wow expansions is that they precede each other by two years, meaning the worgen will appear alliance side two years too late to become a Death knight, as mograine and such are palnning to leave the world once we reach Ice crown Citadel, they say it themselves.
im tired now so people who cant accept change begin flaming me as usual.
While Sargeras' Avatar does exist in azeroth, his actual spiritual manifestation and current host reside in the legion's homeworld. i do not expect him to make an appearance in the maelstrom. i can also say that this expansion's development commenced in march 2009 and is expected [estimated] to be released in october of 2010.
In addition thanks to obox for the info on gilneas. I really didnt think about that but it makes sense.