This may lay the groundwork for Apple's rumored tile-like tracking tag, although there's nothing strictly linked to trackers in the leak.
This would not be the only developer-focused addition, of course. Siri would support a host of new third-party apps, such as media controls (third-party services on the HomePod, perhaps?), Search, voice calling and travel information. There's talk of a "brand new" framework for augmented reality, including an app that allows creating AR experiences visually instead of through raw code. Developers could make better use of the Taptic Engine in newer Apple devices, and Marzipan (Apple's iOS-to-Mac app framework) would let them use Mac-specific features like the menu bar and multiple windows.
There are still plenty of unknowns about Apple's intentions for iOS and macOS at WWDC, including the possibility of major interface overhauls. Hardware news, if any, is a mystery as well. If the sources are on the mark, though, there will be some genuinely functional improvements that might not be flashy, but could have a far-reaching impact on how you use your devices.