Nomura said right after KH2 was released that Sora wielding one Keyblade most of the time was because (in his opinion) it's not fun to control a dual wielder all the time. Obviously his opinion hasn't changed. So, more than likely Roxas will either only be able to use Oblivion and Oathkeeper on special occasions or as a Limit type system ala Sora's Drive forms.
I'm leaning towards the first, mainly because Axel seems surprised when Roxas uses two against him in KH2. Although obviously, that could mean any of a number of things.
