A few comments on yours before I add my own:

1) Having a command input one-shot-kill attack in a fighting game is tough to balance a combat system around. While it can work, it has to be implemented in a way that doesn't break the game with everyone just spamming their OSK's. I actually liked the stage danger zone OSK's from Armageddon, since they were based on controlling an opponents position and were more visually dynamic than a standard ring-out. I realize though that the stage kills wouldn't fit in a 2D game.

2) I think this is something that they're making strides towards. Sub-Zero using his Kori blades is a good example. I second the push for fighters to be balanced around unique feeling gameplay outside of specials. That's something that would add some serious gameplay depth.

As for my idea:

I really really reeeeally want to see Netherrealm go full force behind and action/RPG along the lines of Shaolin Monks and Mythologies that focuses on interesting but vague events of the past. Something extremely story driven with polished gameplay on the level of God of War or Ninja Gaiden. Not only could this make under developed characters more interesting but it could tie into the events of the ongoing MK fighting games.

1) unique, complex and expansive fighting styles per character with branching combos and diverse brutal throws and grapples.

2) multiple costume slots and a custom costume create mode using parts similar to Kreate-A-Fighter...spanning all of MK and many new costume pieces to create really unique looks for the cast.

3) Return of the Betting System.

4) An Actual Finisher/Move Kreate System...using stock animations, with the ability to edit and link different animations together to make new Specials/Finishers for characters. I think this would make everyone happy if their favourite special move or fatality isn't in the game they can just make themselves, and combined with the the Costume System, people can have their own perfect vision of their favourite character.

With Mortal Kombat, I still feel there's a lot that can be done with it.

Ambience-wise, it should have a dark, gritty feel. I'd like to see a good balance between realistic and supernatural elements. I'm thinking that there should be a realistic base but have the supernatural and mystical/magical elements with it. I wouldn't want the series to go too far towards either extreme.

Gameplay-wise, Mortal Kombat games do not need to be the deepest or most technical fighters. I would like the games to be able to successfully appeal to both casual and hardcore gamers. The games should feel pretty easy to get into but hard to master.

I like that some of the games incorporated martial arts styles, and I'd like to see them return but in a different format. Different martial arts styles could be incorporated into different characters' fighting styles instead of being restricted to just those styles.

For example, Johnny Cage's fighting style can have a base in certain styles of Karate while Kung Lao's fighting style can be based in various Shaolin styles of Kung Fu.

Even if more than one character has a fighting style derived from one or more of the same martial arts styles, they can and should be used in their own distinct ways.

Aside from that, there should be a good sense of balance with each character and between characters. So even if some characters are in the "lower tier", they should be able to defeat top tier characters with enough skill and strategy. The MK fighting games need to have the essential gameplay mechanics and to have them be done well, especially if it's a 3D fighting game.

With the story and characters, some care for them, others do not. I fall into the former category even if there are several flaws. I think that more of the story should be focused on in Konquest mode. I still say that Konquest could be on its own disc so that there is plenty of memory for it.

While I know that MK isn't meant to be taken too seriously, there should be a sense of consistency in the storytelling to avoid contradictions and confusing elements. Also, there should be a sense of consequence when it comes to things like resurrections.

Character-wise, I'd like it if they stay away from 1-dimensional characters as well as stereotypes and overly used archetypes (e.g. hot head). I like how MK draws influences from different mythologies, and I'd like to see more of that. I don't mind the team drawing influences from non-Asian mythologies, but I would like the main influence to be Asian themed.

I'll leave it at that for now.