The Exynos 7420 is shaping up to a monster of a mobile chipset, but if a LinkedIn profile discovered by PhoneArena is to be believed, Samsung is already working on two more processors in the Exynos 7 lineup. The Exynos 7890 and Exynos 7650 are listed as “14nm” and “first 64 bits” SoCs; the part about the Exynos 7650 being the first 64-bit chip is odd as the Exynos 7420 is also a 64-bit chip and will soon go official with the Galaxy S6, meaning it's probably a mistake or the Exynos 7650 is a more advanced variant of the 7420.
It remains to be seen if the Exynos 7890 and 7650 are flagship-level chips. The latter probably isn't, if we go by the naming conventions for Samsung's Exynos 5 chipsets (the Exynos 5260 is a hexa-core chip, for example), while the Exynos 7890 sounds like it could be an SoC that's reserved for devices like Samsung's Chromebooks. At this point it's difficult to be certain until more information on the two chipsets comes out.
