First Seen In: Invincible Iron Man Vol. 5, #25.
There was a time when we would've thought that some of Iron Man's most cutting-edge technology would never be feasible in the more grounded world of live-action films. But with Iron Man 3 apparently diving headlong into the "Extremis" storyline, the door will be opened for where Tony Stark's combined human-machine physiology could take him - Primarily, the creation of the armor he named 'Bleeding Edge.'
More than just an upgraded version of Extremis, Stark referred to Model 37 (a.k.a. the Bleeding Edge Armor) as "what comes next" - an evolutionary step forward, if you will. Where Extremis granted Stark the ability to call the pieces of his armor to him at will - an ability shown in the first Iron Man 3 trailer - Bleeding Edge removed the need for external armor completely.
The armor is actually composed of microscopic nano-machines contained within Stark's bones, able to be called to the surface in any shape he mentally commands. Thereby removing the need to 'suit up' or carry around bulky armor pieces (as dramatic as the process was in The Avengers) allowing Tony to become Iron Man anywhere, anytime.
It also seems about time to re-design the standard, bulky armor design for something a bit more striking. Replacing joints and plating for essentially a second musculature of armor, Bleeding Edge wouldn't just be sleeker or sexier, but would give the character even more ability to emote alongside non-CG actors.
In other words, what should "come next."