^ Better control over the breakup of the mask perhaps? It's not like his time limit has improved to the magnitude of hours, at best it still only lasts for a couple of minutes.
I really hope that there isn't another power up in the form of a transformation, at this point, it should definitely be more subtle, but cero would definitely have to be one of the more useless abilities for him to learn, and hollows (and arrancar) in general doesn't seem to have too have too many abilities in common, like shinigami, they have special skills. The common skills can really be listed in one hand, and many of those skills are either redundant (they're equivalent techniques non-hollows can use), or they don't really fit someone like Ichigo (the traveling powers for example, garganta and negacion), or the practice/ability of eating enemies. If he gains any hollow related powers, I would hope that it's unique to him (it fits his character), and it's not redundant.