If I might add my two cents in, at first I thought this was a bad idea. Mortal Kombat is all about huge bosses you have to beat that shouldn't be selectable. But like the other guy said, take a look at Street Fighter II, 4 bad ass bosses you had to fight, but since they were already there with moves why not make them playable and give players more options? They are now four very popular characters. Make them only selectable after you beat the game with everybody so you can keep the illusion of the all powerful bosses until you are finished and have no need to play arcade anymore. I would rather have more well balanced characters to choose from and mess around with than none at all. If they take roster spots away then forget it, otherwise why the hell not.
Shao Kahn playable? Holy ****ing shit i'm angry. Bosses, although a cool prospect on paper, never pan out in the long run especially online. In our online dominated society, it can't be afforded to have one character completely ruin an online scheme that is meant to have 26 factorial ways for a fight to happen. If we have an overpowered boss (a high possiblity) and bad netcode (also a high possibility), what would stop every user out from using him just to boost? Negs on rank for those who pull simply because of the inevitable loss? You'd be rewarding players who lack skill and those semi-good players who seek to better themselves by fighting every type of player (the turtles, the defensive, the aggressive and the tactical) lose this option by losing all options but to fight aggressive players with Shao Kahn. And then the adage, "If you can't beat them, join them" will come into play and then what? SFIV all over again (not boss wise, but rather single character domination online).
The only appropriate counter for that is to travel offline to face players to better yourself, and in this economy who has the ability (read, "time and money") to travel far to search for ample competition?
I'm aware this is all potentiality, but it is a realistic view of what can happen if one unbalanced character is introduced into a game. Just one!
Additionally, for those seeking fun, although some may disagree, it is generally agreed that "Winning is fun". Simply playing the game will be fun most of the time, but once online becomes dominated by the guys who are having fun causing losses to everyone, it'll just become frustrated and people will quit using online.
And if it is, "just a game" some people do and can take gaming seriously because it is their choice,
as said in the UN declaration of Human Rights:
"All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood."
Seriously, I don't get the problem. MK bosses should be ridiculously broken overpowered monsters... but what's wrong with being able to mess around playing with them offline as an unlockable? It's just a novelty, they wouldn't be like normal characters. It's like God Mode in Doom or something. It just saves people from having to hack the game to mess with this stuff.
I wonder if all of the people that hate the idea of him being playable hate M. Bison? That is still the best balance of both a boss and a playable character of any fighter ever, and proves its possible. You can take a character that deals damage in scale to the selectable characters, have the computer A.I. play loose and cheap with him, but have his move set and damage be on par. To the point that it really can't be replicated by most average to above average players.
Its possible for him to be playable but not be ultra broken using the Bison model.