The entire keynote will be iPhone? They haven't done that in a while. Although they did just go over watchOS in WWDC.
WWDC debuts all OS platforms. Debuting watchOS during the keynote doesn't mean anything or indicate a new Watch is imminent. For Example, last year, it was heavily rumored that a new Apple Watch was going to launch during the same time as WWDC 2016, that never happened. Whole point of WWDC is to give the developers an overview and start the beta process before the worldwide public launch in September.