The N55 will be retired in favor of the upcoming "modular" six cylinder. Presumably the six will be an I6, although the possibility for a V6 does exist:
In the interrim, I would expect the N55 to keep pace with the competition. It already makes 320hp in the 740i/iL. I would expect it to hit 350hp in the next few years, before it is finally replaced mid-decade.