At an event today, HTC's vice president of product strategy Bjorn Kilburn noted that the company had conducted research last year to find out whether customers preferred thin smartphones to those which compromised thickness for better battery life. The answer, interestingly, was that they generally preferred thinness, at which point its plans for 3,000mAh-plus devices were removed from the roadmap.
Motorola famously hedged its bets with the Droid RAZR, opting to release two versions: an ultra-thin model with merely reasonable battery life alongside the thicker RAZR Maxx with enormous run time. Considering the precedent that HTC has set with the One X and One S — both under 9 millimeters thick — along with its focus group research, it would seem there aren't any mega-battery models in its near future.
That said, Kilburn notes that battery life is still important, but improvements are focused elsewhere: new battery technology (which is still moving at a glacial pace) and better power management in software, for instance. He also points out that the One X features a larger battery than its predecessors in a thinner frame — a win-win — but don't expect a One X Maxx.