I agree with the Witches of Dathomiir as well as Dark Jedis would be cool, they could make it a night ac or something where if your dark side points are high enough you could chose to become sith or a Dark Jedi who uses the Dark Side but does not accept the sith.
They should also make a class that primarily uses electrostafs/ viroblades cause there are a lot of them weapons kicking around but the are not really significant at the moment.
Sadly, Witches of Dathomir weren't formed as an organization until 600BBY. :/ That fact depresses me constantly, and I have to remind myself of it when making Sith characters all the time as a result...
EDIT: Fully agree with your second point, though - a player class that makes use of electrostaves/vibroweapons/techblades would be fairly awesome. I sure eat enough of them to the face.