what would be cool is if when you meet a sith lord you had a choice of either fighting or accepting a task to assasinate a rival. then as you complete more tasks you gain more respect and can eventually take over that sith clan.
sort of like that woman in Bounty Hunter, she was a prisoner then took over the whole group.
this idea could work, as in kotor 1 you could keep going back to Dantoeene as a 'base', and talk to the jedi masters. perhaps here you can keep going back to a sith master.