Seeing Scorpion punch Sub Zero's face every time I'm taken to the main menu is horrendously annoying.
I would like to see Sub Zero catch Scorpion's fist, and break or cut off Scorpion's arm.
Have every character appear randomly in the main menu, with a 50-50 percent chance of one move prioritizing over the other.
To better explain: There's always a closer character, and a farther character, as if it were a pokemon battle. The closer character has a set attack animation, and the farther character has a set attack animation. 50-50 percent split in which character is shown succeeding. Thus would be much better than Scorpion and Sub Zero all the FUCKING TIME.
To move on to things that actually make sense: The game should ask you who your favroite character is, and change the look of the main menu based upon which character is listed as your favorite. For example, if the user's favorite character is Sub-Zero, the menu would turn light blue, possibly with a picture of Sub-Zero launching an Iceball, or Raiden's menu being covered with Lightning, or Scorpion's covered with fire, or Johnny Cage's covered with money. (All of which have a nice picture of the character as well.) Also, being able to mix up character's or alliances for your main menu would be amazing. This concept is seen in Playstation All Stars.
This "favorite character" concept could also be utilized in online matchmaking. Next to an online player's username, there could be an icon that displays the user's most played or favorite character, allowing the players to avoid fighting Noob Saibot or Kabal online, or search for the matchup that they need help in.
Also useful would be the ability to enter combat codes from the character select screen, and mix together as many kombat codes as the players wish.
No blood, plus no foreground elements = far less lag. Very useful online.
The characters should have different loading screen pictures and character select screen pictures based upon which costume the player chooses to wear.
A team system would be very useful as well, for reasons that are shown in my "Injustice: Gods Among Us Wishlist" video on AmazingGamingChannel. You'll find more stuff there.
Remove the ability to spam chat room lobbies through the use of pre-set text-based messages.