I don't think they could get away with dropping this "True Sith" Plot. They just built up too much of it. The game has to have something to do with Revan, or something Revan did, or at least wherever he went.
A new Jedi order will be stablished by the Lost jedi children. So why not skip a few years and start with that new order?
I don't see how another Jedi Order could be started. By the end of K2, all of the Jedi masters were dead except for Atris, and she wasn't even a Jedi at all. The only actual Jedi who we know survived was Bastila, and she was just a padawan. She couldn't rebuild the order. Potentially, I suppose the Exile's companions could build another order, but that's only if they're light-sided. Therefore, all evidence seems to imply that in the Dark Side ending of K2, the Jedi are screwed.