I upgraded from the 216+II that I bought only a week ago, not realizing this was about to be announced. Still finding my way but I can't say enough about how easy to setup and use these are.
PLEX: Right now you need to install the Plex app manually, which is easy. You download the Synology package from the Plex website, Intel - 64-bit (DSM +6.0), and then select manual install in the package manager on Synology and choose the package you downloaded. Super easy.
UPGRADING: I pulled the drives out of the 216+II and put them straight into the 218+ and it fired right into a migration tool. No data or user account loss. I had to manually setup the Connect.to and dynamic DNS again to point to this new box, but recognized that I had a new box and removed the old one from the record. YMMV, but very straightforward.