It was a "joke ending" and nothing else,there's no more than that for Reiko's Mk4/Gold ending.

How do you know it was a joke?

The MK team themselves have admitted little thought was put in Reiko's ending. Either of them.

His original ending where he just strolls into a portal was just a joke. They later added on the part where he puts on Shao Kahn's helmet to "add intrigue to his character."
I'm guessing whether or not he was meant to be Shao Kahn depended on fans reaction. Most fans hated it, so it was dropped.

And Shao Kahn's Deception bio states he created a decoy clone of himself and that was what Quan Chi and Shang Tsung actually killed.

Oh ok. That clears up everything. Thanks.

I remember making a thread like this when I first saw the ending... Ahh, memories... Anyway, the issue seems to have been resolved, so I'm going to close this.