Some good news and bad news, let's start with the bad. Mortal Kombat: Armaggedon will be the last chapter of the series to be on current gen consoles (PS2, original XBox). Creative Director Ed Boon said "This is the last Mortal Kombat on this generation of consoles, and we also wanted to end this kind of fighting mechanic for Mortal Kombat."
Now, before you start bemoaning the end of the series here's the good news- there will be another Mortal Kombat game, this time on the PlayStation 3. Some characters will be getting replaced by new additions and a new fighting system wll be in place. Plans are in place for taking advantage of the new console capabilities to provide players with new presentation and graphics. Just about every aspect of the game will be new.
Boon didn't say which characters are being replaced but it shouldn't be too long before that word is leaked out.