Very little has been confirmed, so take this all with a grain of salt, but based on the latest leaks/rumors here's what to expect:
SD Card Slot: Yes
It appears Samsung was unable to make its Exynos 5 octa-core big.Little chip work and switched it out for a Qualcomm Snapdragon 600. Rumors indicate the big.Little setup was causing thermal efficiency problems and was also a battery hog. It's disappointing Samsung couldn't make it work, but the Snapdragon 600 is still a beast of a chip so it's not much of a downgrade.
Even more surprising though is that it looks like the Galaxy S IV will have a SoLex LCD screen instead of a Super AMOLED as in every other Galaxy S phone to date. The SoLex screen is very similar to the Super LCD 3 in the HTC One. Considering how much marketing effort Samsung has put into its AMOLED screens it's a shock to see its flagship smartphone arrive with an LCD. Again, it looks like Samsung was unable to get sufficient yields of 1080p AMOLED screens or suffered some kind of unknown quality issue. While the Super LCD 3 can't match the deep blacks and contrast of an AMOLED screen, it features superior color accuracy and clarity by virtue of its true RGB subpixel matrix.
As far as battery size the GSIV looks to feature a removable 2600mah battery which should easily power through a normal day of use. Standard internal memory is rumored to be 16GB with 32GB and 64GB as options. The GSIV will also have an SD card slot for expanded storage. Finally the GSIV is rumored to feature a 13MP camera utilizing a Sony sensor. Samsung has a reputation for excellent cameras and the GSIV should be no exception.
Overall the Galaxy S IV looks like it'll be an extremely well rounded smartphone. The hardware checks all the flagship boxes and although it's more of an incremental upgrade in a lot of areas the whole package (as rumored anyway) looks formidable. We've also heard rumblings that the GSIV will make expanded use of gesture controls and may incorporate some kind of health monitoring system into the software. Samsung does an excellent job of mixing unique features with excellent hardware and that's what makes the Galaxy S series so popular. In 16 days we'll know if they've done it again. I'm cautiously optimistic.
UPDATE: This morning it leaked out that the international version of the Galaxy S IV may indeed use the Exynos 5 Octa chip, while the U.S. variant will use the Snapdragon 600. This is very similar to what happened with the Galaxy S III. The Snapdragon 600 features an integrated LTE modem and is more power efficient than the Exynos 5, which would require a separate chip for LTE. Since most international markets don't have mature LTE yet, this isn't a consideration for them.