Besides the usual upgrades that are expected, like faster Exynos 8890 or Snapdragon 820 chipsets, and a higher-resolution camera, we've also heard that the Galaxy S7 might feature a larger screen, and two versions could be launched concurrently - one with a 5.2" flat display, and a curved dual-edge S7 with a larger, 5.7" screen.
As if to confirm that there will be indeed distinct variations of the Galaxy S7, a firmware leak has listed two software version - G930FXXU0AOK6 and G935FXXU0AOK6 - that are said to commence development as soon as this month. The Galaxy S6 is coded internally as SM-G920, while its sibling with flexible display, the S6 edge, is marked as SM-G925, so the aforementioned firmwares starting with G930 and G935 could indeed be their successors, announced together again, leaving the eventual Note 6 and S7 edge+ for the second half of 2016.
Last year, the final firmware work for the Galaxy S6 didn't start until later in December, so we might indeed see the S7 announced in February, as rumored heavily, instead of March at the MWC expo. If the Note 5 announcement three weeks before the IFA expo this year is any indication, we might see the Galaxy S7 announced as soon as the first half of February, so the rumors and speculation about its final shape and specs can only grow from here.