Source: Moscone Center
Spotted by MacRumors, the online events calendar for Moscone West -- Apple's usual WWDC venue -- shows a five-day window blocked off for an unnamed "Corporate Event" to be held from June 8 through June 12, 2015.
The generic title is not a guarantee that Apple will hold WWDC 2015 on those dates, but there is a moderate chance that the rumor is accurate given the remainder of June is taken up by conventions and trade shows. In previous years, Apple has secretly saved its usual June window by disguising the conference as a "Corporate Meeting," a term used in 2011 and 2012.
If Apple keeps to an annual product update cycle, next year's WWDC will likely bring iOS 9, a new OS X and possibly hardware, though nothing is a lock at nine months out.
For the most recent WWDC, Apple was able to keep a bulk of its software initiatives secret until the big reveal on June 2, including iOS and OS X continuity features, iCloud Drive and a completely new coding language called Swift.
Also introduced at WWDC 2014, and slated for release this fall with iOS 8, were Apple's health and connected home initiatives, dubbed HealthKit and HomeKit, respectively. The upcoming software will allow iPhones and iPads to become central hubs for data aggregation and offer control of other connected devices like automated home appliances, health tracking products and more.