The new mechanic I had in mind was a swing radius. Three different types- one narrow, normal and wide, with degrees of perhaps 45, 90 and 180. I feel this would give the player more controll over where their weapon is moving as well as add variety in combat for those focussed mainly in the up close and personal approach.
The narrow swing radius would be ideal for when companions and friendly helpers are caught in the fray of battle, allowing the player to focus their attacks. With this shorter swing radius would come, idealy, more speed with their attack, serving not only as a way to avoid friendly damage but providing a tactical choice in combat. This radius could also possibly incorporate upward and downward motions and maybe even some forward jabs, all still fitting into the desired confined area. The weapon of choice I think would be a dagger as the combined speed would prove difficult to avoid, though the increased speed could also be used to compensate for the lesser speed of slower, heavier weapons.
The normal swing radius would be like the swing radius of past games and would provide a balanced mixture of speed and sideways range. Ideal for situations of medium proportions and while alone or out of range of companions, for your's and their's sakes. I would think that shortswords and longswords, as well as any blunt weapons that fit into the category of medium length, would be ideal for this swing radius.
Finally the wide swing radius would give the player a large arc to throw their weapon in. This radius would be ideal to use when against large hordes of enemies when alone or perhaps against very large enemies such as the dragons indicated by the teaser trailer. Speed would of coarse be greatly decreased but serves the purpose of preventing flanking in close quarters as well as keeping the tide back. I think the weapon of choice would be a claymore, battle axe or warhammer due to their long reach.
Ways to provide a very friendly and streamlined way of access to this feature, if considerable, would be as an optional hotkey ability just as spells and, if I may, the ammo type hotkey in Fallout: New Vegas is. Simply press the hotkey once or twice to get to the desired swing radius and hack away. Different abilities or perphaps the entire swing radius itself could be obtained or unlocked through different levels of mastery with the skill of the weapon in mind. Could power attacks be incorporated as well? Up to you to decide.
Overall I think this feature would provide ways to fight safely amongst comrades in arms, tactical choices for different combat situations and variety in fighting style. Please let me know of what you think as I posted this here to see the reactions of fellow gamers before promoting it any further. I am open to comments and suggestions, and please pardon any grammatical errors I may have made. Thank you for your time. I expect great things from this game.