Rumor has it that Samsung Galaxy S4 will be unveiled in January at CES 2013 event and that it will pack a full HD AMOLED display with a diagonal of 5 inches and a resolution of 1,920 x 1,080 pixels, which will bring a pixel density of 441 ppi.
If you asked me, I would say that the Samsung Galaxy S4 release date set sometime in February - March time frame (after the official announcement at CES 2013) it would be a rushed one, and the sales of the new Samsung flagship will be cannibalized as soon as Apple will unveil a new iPhone model. Apple will probably launch the iPhone 5S or iPhone 6 in September 2013, so a Samsung Galaxy S4 hitting the market half a year ahead of the next iOS smartphone would stand no chance in front of it.
In my opinion, the best way for Samsung to launch the new Galaxy S4 is to set the release date in early Q3 2013, like they did with the Samsung Galaxy S3. Then, the Samsung Galaxy S4 will have enough time to outsell the iPhone 5 and it will still be a fresh device in the battle against the next-gen iPhone.
As about the technical specifications of the Samsung Galaxy S4, the South Korea-based company will probably fit a quad-core processor based on Krait or Cortex A15 architecture paired with Mali-T658 MP4 GPU with eight cores. We are talking about the Exynos 5 Quad chipset clocked at 2.0 GHz. The smartphone might also have 2 GB of RAM and a 12 megapixel camera.
I am also sure that Samsung will not make the same mistake it did with the Exynos 4 Quad SoC underpinning the Samsung Galaxy S3, which isn't compatible with the LTE networks in North America. This year, Samsung had to replace the quad-core processor of the Galaxy S3 US variant, with a LTE-friendly dual-core Snapdragon S4 chipset.
Samsung Galaxy S4 will most likely run Android 4.2 Jelly Bean out of the box, as the company's software engineers won't have enough time to customize Android 5.0 Key Lime Pie with Samsung's proprietary TouchWiz UI.