There are certain players throughout the NBA capable of shifting between the 4 and 5—Kevin Garnett and Tim Duncan come to mind—but Superman isn't one of them. He can flash those pearly whites of his and pretend everything will be fine all he wants; he's not fooling anyone.
Even traditional power forwards must be able to score outside of the paint, which Howard can't do. Neither can Omer Asik. Both inhabit the same, confined space. Playing them alongside one another will be a floor-spacing disaster that has the potential to render a once-potent Houston Rockets offense anemic.
Rather than shifting Howard to the 4 and watching their title ambitions perish beneath a faulty offensive prototype, the Rockets should take to the trade market and acquire a stretch 4 who makes sense. Howard is at his best surrounded by shooters (see the Orlando Magic), not when he's tasked with playing next to a more conventional tower (see the Los Angeles Lakers).
Houston has the assets to make a splash, too. Furnished with a number of promising young prospects and two potential starters on almost-reasonable contracts (Jeremy Lin, Asik), the Rockets must think big—so that they can run small.