I always sort of assumed that goblins were degenerated Altmer.
Yes, thats a favorite theory of mine as well.
We know the elven form in general is rather fluid, they seem to change from one species to the next at the drop of a hat.
Altmer are said to have extensive breeding laws and a value racial purity greatly.
Perhaps this is because if they do not practice these things they will follow the fate of the Aldmer and change into something else.
I always thought the goblins of Cyrodiil were what was left of the Ayleid.
With their civilisation destroyed and them driven away or underground they would not have their genealogy records anymore and likely times were just too harsh to care about more than basic survival.
Altmer were close to Ayleid. I think they were sometimes called the heartland High Elves.
I agree with the idea that slavery in Summurset could still exist, only the Altmer dont see it as slavery, much like we dont think of a horse or oxen as enslaved.