It works perfectly in the Bourne films given they're fast paced action movies that emphasize realism over big spectacle. A film about men who shrink down and go inside the human body, though, is kind of big on spectacle. One would expect a film of that nature to be shot with a less-frantic style that allows plenty of time (and space) to take in the sights. Obviously it's not impossible to mix handheld photograph with bold special effects, but I'd hardly call it ideal. I'm not even sure I'd call it desirable. It works in District 9, but what makes Neill Blomkamp's film so great is how unique that particular blend is. It'll be boring if everyone starts to ape it.
Landau's comments made it clear that the trio have yet to agree that this style is best for the film, but he seems confident enough in his director that it may end up being so. If that's the case, combine Greengrass' style with James Cameron's 3D mentorship and Fantastic Voyage is bound to be a memorable experience; if only because it causes those prone to motion sickness to get a closer look at their own insides.