A new race might not be entirely off the table.
When asked about whether viera and hrothgar would be the last new races to be introduced to the game, and if there were any plans to add more customization options to the established races, Yoshi P responded like this:
"if it is a customization option that significantly changes the shape of the races body, I think we would be better off to tackle the challenge of just introducing a new playable race all together instead."
Source:
Link
Also, they probably won't show female hrothgar/male viera NPCs unless they are prepared to make them playable. Viera and hrothgar NPCs were not given head items at the start of ShB because the dev team was aware people would then ask "why can't we wear head items then?" This was a concern Yoshi P expressed in one of the live letters - the same logic can apply to the other genders as well. If we do see a male viera or female hrothgar NPC, then it would be safe to assume they will be playable options later.