Races are actually probably easier to add than classes. Humans will be the baseline. Adding a new race just requires some kind of differentation, but not necessarily any new skills. Adding a new class would require a ton of new skills, which is a lot of work.
For instance:
=Humans=
Hit points: 100 + 20 / level
Energy: 20, 2 basic regen
=Dwarves=
Hit points: 150 + ( 20 / levels 1-10) + ( 30 / levels 11-20)
Energy: 10, 2 basic regen
+20 armor vs. Earth.
-20 armor vs. Water
(So, a non-linear hit point gain; when you reach level 10, you get +20 hitpoints, and when you reach level 11, you get +30 hit points.)
=Charr=
Hit points: 100 + 20 / level
Energy: 20, 2 basic regen
Gains 1 energy after activating any Attack, Stance, or Preparation skill, or casting a Fire, Air, Death, Blood, Smiting, or Domination spell. All other skills cost +1 energy to use.
=Mursaat=
Hit points: 50 + 15 / level
Energy: 25, 3 basic regen
None of those would require difficult coding. The artwork isn't unreasonable for one race per expansion pack. Balancing is a larger issue, but certainly possible. The hardest issue is the design issue of how to insert the race into the game. Do dwarves suddenly show up in Pre-Academy Ascalon? Seems unlikely. Where do they show up? How do you work them in to the Chapter 1 storyline? Maybe you don't.
Some hard questions regarding storyline. The rest is fairly easy, I think.
Mind you, those examples show a very simple way they could add interesting new races. Obviously, races could get skills associated with them, or any number of other interesting things. However, even the relatively small changes I used for examples would play very differently.
Of course, some of them are slanted towards one class or another, but so be it; it would be hard to make races that are actually different without it seeming to slant them in one direction or another, and it allows for some fun when people "go against the grain" and make a Charr Monk Healer.
Other ideas welcome, especially ones that talk about wildly different ways to do races or bring them into their story...