Consider... Ironmonger showed up in the last 15-minutes, or so, of the movie... and they had a fight scene that was more a ham-handed mauling, than any kind of dynamic, hi-tech clash. That fight scene did not consume the breadth of combat sequences thet IM can have with another armored baddie. I really think this hand-wringing over "another armored villain" is misplaced.
IM was a origin film... IM2 will be a development of the world around IM... including competing industrialists, unscupulous mercenaries, and the dangers of Stark's chosen path. Having another armored competitor is entirley appropriate.
The distinction that could make CD different than IronMonger (if it is indeed to be CD), is that CD's story could focus more on the idea of mass production and distribution, for major government contracts. Stark would be out to get CD and shut down the operation of trying to arm the world with this stuff... as opposed to IronMonger being out to get Stark, as a power play. Hammer has made CD as a new product to compete in this new age of weapons technology... Stark understands the folly of putting this kind of technology into the wrong hands.
Moreover, CD could be operated by a seasoned pilot and trained fighter (not a corporate suit, who's drunk with power)... the ariel battle sequences are ripe to be nothing short of spectacular.