Samsung may put one of its recent 8 GB modules into the Galaxy S8, that are being manufactured using the 10 nm process, a usually quite reliable user on Weibo recently said. Faster UFS 2.1 storage may also be part of the package.
http://www.notebookcheck.net/Samsung-Galaxy-S8-might-come-with-8-GB-of-RAM-and-UFS-2-1-storage.189048.0.html