How expansion to the ending of Sith Edition should be...(SPOILERS)
After the events of Sith Edition, Lord Starkiller is going to go after Palpatine for sure. This is how I would envision it.
The two Sith Lords clash in a epic battle with flashing blades of energy and crackling bolts of lightning. Just when it seems that they are to evenly matched, Lord Starkiller buries his blade into Palpatine's chest followed by a violent force push hurling the Sith Lord across the room.
Mortally wounded, Palpatine clutches his chest and stares up in shock and confusion at Lord Starkiller, who now has all of his armor torn away revealing what he looks like underneath it all. (cybernetic reconstruction skin dlc)
Palpatine: Impossible! You should not be this powerful!
Starkiller: Why? Because I am more machine than man? (Evil laugh)
Only now at the end, will you understand. The force does
not reside from within the flesh. It is not from your precious
Midi-chlorians. We draw our power from within our spirit. That
is our true connection to the force. This cybernetic body of mine
has only made me stronger. It gives me more pain, more hatred
and I feed from that. When you crashed that ship down upon me
it took everything from me. The people I cared for...my body.
I had nothing left...nothing but the dark side and that welcomed
me with open arms.
Palpatine: (pained crackling laughter) Then it would seem that I have
succeeded after all. The Sith will remain strong with you. Now
my apprentice, strike me down and take my place as the Master
of the Sith!
With a gesture of his clawed hand, Palpatine was lifted to his feet and in a swift slash of saber, Lord Sidious's head was cleaved from his body. A massive explosion of dark energy decimated everything around it, everything but Lord Starkiller. In the middle of the carnage stood Lord Starkiller, the new Master of the Sith.