The Snapdragon 820 is still new and shiny, being hailed as "cutting edge" by tech publications and treated like the very peak of mobile chipsets at the moment. Qualcomm, however, doesn't seem like they're going to be slowing down anytime soon, and information about the new chipset is already starting to surface (via NPU).
This comes from Microsoft's list of processors from Qualcomm that are going into Windows 10 Mobile, which now includes "MSM 8998," which people are rightly assuming is going to be the Snapdragon 830. The 820 chipset was referred to as the MSM8996, and the 810 chipset before it was dubbed the MSM8992, so it only stands to reason that the pattern is going to continue into the next Snapdragon chipset.
Beyond the fact that it's being made and will be supported by Windows 10 Mobile, we don't know much about the Snapdragon 830 for sure. It's a fair assumption that it will be a great deal faster and better-performing than its predecessors - especially since we know that Samsung will be manufacturing it, and likely with the 10nm chipsets they're beginning to mass produce.