Samsung is reportedly interested in launching a new flagship relatively quickly, so as to counter weaker-than-expected S4 sales. The S5 is said to feature a 64-bit CPU (Apple just put one inside the iPhone 5S) that (like the Exynos Octa) contains eight cores and leverages ARM's big.LITTLE architecture, as well as a 16MP camera with optical image stabilization.
Though easily the best-selling high-end Android phone, S4 sales have been pressured by a mix shift towards low-end/mid-range smartphones, a large portion of which are sold in emerging markets where many consumers can't afford phones with $500+ unsubsidized price tags.
Going forward, Samsung and other high-end vendors will also have to contend with mid-range Android phones featuring high-end specs. Xiaomi's MI3 is one example; LG/Google's Nexus 5 might soon be another.