That may be their role in the game, but the biology begs to differ. Falmer are nothing like goblins; that's just how we treat them. Goblins have existed in both Morrowind and Cyrodiil, therefore it wouldn't be surprising to see them show up in the warmer regions of Skyrim. However, the little people in the trailer aren't goblins; they're http://www.uesp.net/wiki/Lore:Riekling#Riekling. These absolutely fit into Skyrim because the Nords thought they're a varient of the Falmer. Whether of not that's true, they still fit right into the climate, and having more variety is more than welcome.
I can't really agree with adding Ogres to Skyrim. I think they kind of fall into that "not common" category. However, boars should be everywhere.
There is a theory that Goblins are devolved/ evolved elves.
We know for instance that elven races are prone to rapid subgradiation. They tend to become something else at the mystical drop of a hat.
We know that Altmer, who are closest to Aldmer, have breeding rituals and customs that would likely seem restrictive, harsh and eugenistic to us. But there could be more behind these practices than simply bigotry and belief in self-superiority.
It could be that the Altmer have retained their semblance to the Aldmer
because they have these practices and do not allow anyone to reproduce with anyone on a whim. It could be that Goblins is what happens if they
stop those practices.
It is also not beyond the realm of possibility that the Goblins we encounter in Oblivion are what is left of the Ayleid.
With their empire, society and civilisation broken the remnants of the race either assimilated into Imperial culture posing for Altmer (like Umbacano), fled to inhospitable areas where at that time they still had settlements such as Black Marsh and, importantly, retreated to the caves of Cyrodiil. Their mythic identity, their pride shattered they perhaps lost their ancient practices, adapted to the underground and became Goblins.
Lastly, there are the Betrayed (Falmer) in Skyrim.
Knight-paladin Gelebor, likely the last true, unchanged Falmer (or an image of one as there is speculation he is an avatar of Auri-El really), his dialogue about the Betrayed indicates that it couldnt have just been what the Dwemer did to them that caused their current form and mind alone.
Again, after their defeat by the Nord and betrayal by the Dwemer the spirit of these elves was broken, their customs lost.
Perhaps they adapted to their new environs, their new myth, and became the distinctly Goblin-like creatures we see today.