They have a lower-half snake body, so from a developer's point of view, it would be too much extra work.
Very true and I do not expect to see them from a stock-game as development time is far too limited and equally precious to include a race with a completely separate set of animations.
I do expect to see at least some race from Akavir (the Tsaesci being the race that has had the most influence on the rest of the world of Mundus) as lore-wise they would be perhaps the most interesting races to explore.
Mayhap some corners could be cut (e.g. Morrowind beast race) and have it shipped as a DLC/Expansion where time is not of the same amount of essence.
Bear in mind that this is mere conjecture and surmisal.