It's not going to be the Apple Watch +. Next year is an "S" year. It'll be the Apple Watch S. Followed by the Apple Watch 2, Apple Watch 2 Titanium-With-Gold-Accents (Early 2017), Apple Watch With Retina Display (Late 2017), Apple Watch Air 3, etc. etc.
It's funny how Apple isn't a big fan of reliable model numbers and just describes what something looks like when they do a mid-model revision. Even Mercedes and BMW have letter and number designations, and that's who Apple seems to emulate on the conspicuous consumption spectrum.
(Disclaimer, I actually like some of the stuff Apple produces, but I'm not a big fan of the premium they charge. I do, however, recommend their phones and computers to people who just want working maintenance-free systems for home.)