A technical specification document has shown up on Intel's website laying out the specifications and internal design of the upcoming June Canyon NUCs. The CPU and wireless card are soldered on, but the RAM and storage are upgradeable on two of the models.
https://www.notebookcheck.net/Specs-leak-for-upcoming-entry-level-Intel-June-Canyon-NUC-supports-two-4k-displays-at-60-Hz.280606.0.html