Assuming that 2K Games is already working on a BioShock 3, IGN has whipped up a two-page editorial that asks the publisher to rethink some of the series' mechanics and bring something fresh to the table rather just than another shooter-heavy slog through Rapture.
...the gameplay hook for almost all of Bioshock is the integration of Eve-powered plasmid abilities. However, it's not going to be enough to simply keep ramping up these powers how many different ways can you fry, freeze and levitate something, after all, before you're scraping the barrel? With that in mind, we think simply dotting the plasmid lines won't suffice. We need a new take on things. And no - we're not talking about playing as the Big Daddy again or Big Sister, for that matter. So create a BioShock that's actually a worthy successor to System Shock 2? Sounds good to me.
Instead, weapons and combat are going to need a rethink. Perhaps this is tied to a better player growth system not simply unlocking new plasmid slots, but actually having a broader and more tangible player growth system. Really, taking a few cues from System Shock 2 or other richer role-playing games might not hurt.