The main point of contention with this topic is the clear divide in what NPCs and PCs are capable of in regards to racial interactions -- namely the massive gap between what is said to be allowed for a race compared to what a player can actually accomplish.

Marriage.

Taking into account all the NPCs in the game it is shocking there is so little variety from the point of view of the lore and even more shocking is the smaller amount of marry-able NPCs among these (not very)-varied races.
The race with the most marry-able NPCs is the Nords; this is acceptable as Skyrim is their home province.
The races with the least marry-able NPCs are the Altmer, Bosmer, Khajiiti, and Redguard. This is where it gets slightly strange.
It makes sense for the Altmer to have few marry-able NPCs since they were recently at war with the then-disintegrating Empire.
It makes less sense for the Bosmer or Khajiiti. Surely there would've been some members of these races seeking to escape war by fleeing to other provinces, then there will likely be all the escaped slaves from people fleeing Morrowinds and Vvardenfells destruction. As for the Redguard I'm not fully sure on their involvement in the Altmer/Empire war.
However all of this does not apply for an Altmer, Bosmer, Khajiiti or Redguard PC of either gender -- as the PC can marry whichever race of either gender he or she wants -- though with exceptions being Bosmer and Khajiit for which none are available to marry and Altmer and Redguard for which only one of each of these races is available to marry -- both of them female.

Though if its a Nord you're after go hog wild.

Trading, property bartering.

To add onto the rather strange stance towards marriage, it seems they cannot make up their mind about which race can or cannot trade. Khajiiti NPCs can be found outside the cities complaining that they cannot enter to trade whereas Khajiiti PCs can easily enter any city to trade or even steal from; which makes the guards seem foolish for allowing in a thief but not honest traders.

General.

A lot less racial variety than in Morrowind and even Oblivion. Yes the home of the xenophobic Dunmer in Morrowind was more racially diverse than Skyrim -- likewise was the dull middle-fantasy land of Oblivion more diverse.

Dunmer - Do not sound like Dunmer, gone are their gravelly voices of yore, now they sound sort of British.