is a martial art in the SW extended universe designed by a culture that got screwed by the Jedi once and decided to find a way to counter them. They learn how to mask themselves from the Force and turn their fists into lethal weapons. It's pretty much Star Wars Kung Fu.
The time frame on it is appropriate for the game time frame, at least as a reasonably fresh discipline (it was developed some vague time frame before the Old Republic Era), but the problem, as I see it, exists insofar as Teras Kasi is pretty much defined as being an anti-Jedi fighting style developed by a culture pretty much defined as being anti-Jedi. There is some evidence that Teras Kasi was used by some Jedi/Sith, but there's some question as to how exactly they learned it. The problem, overall, is that it would be difficult to explain exactly why a Teras Kasi master would join either the Republic, which has Jedi actively involved in its governance and upkeep, or the Empire, which is explicitly run by the Sith.
The more likely class, as I see it, is having an Echani
combat specialist: light/medium armor that uses vibroblades and fist weapons (the game has some artefactual remnants that suggest that fist weapons existed at some point and have the baseline code laid out for the eventual implementation). Depending on how the developer's feel like fleshing it out, the mirror classes could be identical (Echani Fighter) or split between the Thyrsians (Sith cultists) and baseline Echani (generally considered to be Republic sympathizers or close enough). It would still provide the whole "fist weapons and martial arts" class that people would want from Teras Kasi while having fewer problems within the confines of the game universe.