This is like when fanfic writers force their OC's into an already established world. Like Art Lean in the first movie. Let's hope he'll share the same fate as Art did.
How dare you!
I don't mind original characters if they're on the sidelines, like I actually enjoyed Art Lean's presence because it actually fleshed out the world building in terms of it representing some of the best martial artists from around the world competing in a tournament. Likewise, I enjoyed meeting Johnny's sensei (well, sort of...), Liu's grandfather, seeing one of Shang's monks fighting Liu etc; gave it that classic Bloodsport feeling of the tournament is much bigger than our main characters (in fact I'd have liked to have briefly encountered a few more of the dozens of every-day Earthrealm fighters getting off the dragon boats to be honest). That way you can kill of a good guy without having to murder a beloved main character; the key point was that they were nice little roles that just gave the main characters and tournament a bit of a larger scope.
In fact this is a point of why MK '95 worked so well (yes I know it's cheesy pulpy trash, but it works and has a good character ensemble) because it knew to not overload the plot with characters; it went for a classic martial arts tournament movie structure and did it perfectly serviceably and just brought in a few new side characters to flesh out the world.
Mortal Kombat Annihilation on the other hand threw in every character they could from MKs 2-UMK3, with even two from MK4, for no reason other than to flood the screen with a relentlessly obnoxious attitude of "HERE ARE CHARACTERS YOU KNOW!!!! DOESN'T MATTER WHY THEY'RE HERE, HERE'S MORE CHARACTERS YOU KNOW!!!!"
Mortal Kombat 1995 had 12 characters from the games with a few outsider original characters to expand their world and for me felt just right... Mortal Kombat Annihilation on the other hand had 24 characters from the games, everyone was connected, characters perform random plot roles without any explanation, and the movie is an utter a mess. And they also murdered Johnny Cage.
So I'm not against any original characters being in the movie, however in spite of what I've said above, if this is going to be an Alice in Resident Evil situation, where they introduce a new main character for no logical reason, well then I won't be keen.