I woke up faintly remember bits and parts of it. It was about a month after the game was released and Ed Boon publicly announced how to unlock 1 of the super unlockables.
It had to do with going into options and changing the difficulty, and beating the game with a specific character in a specific costume in a specific difficulty.
After this first character was unlocked, there would be a hint on how to get the next character. The character that I unlocked first in my dream was Kano. I had to beat the game on easy mode with Kabal's alternate costume.
I know this is probably not how to unlock them, but the simple-ness of the dream caused me to think that maybe we're over thinking the process of unlocking Super Unlockables. Maybe it's something that we see all the time in the game, just never thought it was worth our time to try it out.