The mortis gods would be a terrible addition to the game. If they don't solo every other team in the game -- at the same time, in 14 seconds total -- then they aren't the gods they're supposed to be. What you want the mortis gods countered by ... Grievous? Reva? Let's be serious. They are deliberately unbalanced in the lore. There is no balanced way to add them to a game. It is the WORST idea.
A light side Mara Jade isn't a bad idea. The smugglers that she ran with would enable an appropriate lift to that faction. (Talon Karrde, etc.)
Pong Krell is the best of those mentioned above and Dark Barriss is the best toon not mentioned.
There's better fodder in ships, though. The TriFighter was suggested above and I like that.
But the best addition to ships would be Ventress' Ginnivex FanBlade fighter. Nothing beats it for coolness and Seps aren't terrible but are nowhere near meta, so you could drop an excellent new ship on them and give them a pretty large boost without unbalancing anything.
