With Apple (NASDAQ:AAPL) reportedly shelving any Apple TV announcements the week before what was being predicted to be an Apple TV-centric event, investors and developers are wondering what items will be the main focus during the WWDC 2015 keynote on Monday.

Apple's WWDC 2015 announcement artwork. Source: Apple.

As a developer-focused event, Apple will undoubtedly show off updates to its two main operating systems. But there is less certainty about some other areas Apple is rumored to discuss, particularly a revamped music service, an improved Apple Watch software development kit, or SDK, and improvements to HomeKit.

A music revamp
As the potential main focus of the event, it has been rumored for a few months now that Apple would launch a revamped streaming music service at WWDC. The service will likely tap into technology gained in Apple's $3 billion Beats acquisition last May.

The revamped streaming music service will be "a direct rival to Spotify AB and other popular services that let users stream songs instead of buy them," according to a WSJ report on Monday. 

Just days before the WWDC keynote, Apple is still negotiating terms on the new service with record labels, according to a Thursday report from Bloomberg.

Apple Watch SDK
On Monday, Apple will announce an Apple Watch SDK that gives Apple Watch app developers more possibilities with the device, Apple operations chief Jeff Williams said at Re/code's 2015 Code Conference in May. Most notably, the new SDK will allow direct access to the Apple Watch's built-in sensors.

Apple Watch Sport. Source: Apple

Apple's rapid roll-out of developer tools and hardware access for Apple Watch goes contrary to the company's historical practice of being slow to support native functions for third-party developers. The tech giant's move to quickly give third-party developers greater possibilities highlights Apple's efforts to bolster its app store ecosystem.

There's been little buzz about Apple's 2014-announced HomeKit, an iOS framework for communicating with and controlling connected accessories within a home. But investors shouldn't underestimate its importance. As sales of connected devices continue to soar, consumers will be looking for a central way to control these devices -- and HomeKit is meant to do just that.

It's likely Apple will introduce new developer tools for HomeKit during WWDC, as well as new abilities for the framework. But will any of the new features be noteworthy? A role for Apple TV in HomeKit could prove to be interesting. Chances are, Apple will spend time discussing how Apple TV can be used as a hub for Apple TV.

In a recently released document on Apple's website, the company says users will be able to control their accessories while away from home with Apple TV:

If you have an Apple TV (3rd generation or later) with software version 7.0 or later, you can control your HomeKit-enabled accessories when you're away from home using your iOS device.

Sign in with the same Apple ID on your iOS device and Apple TV, and you'll be able to use Siri commands to remotely control your accessories.

Finally, there's always a chance Apple could surprise the world with an announcement the Apple rumor mill isn't aware of. Last year, for example, Apple unexpectedly announced Swift, an entirely new programming language.

Tune in to a live broadcast of Apple's event by visiting Apple's website at 10:00 a.m. PDT on Monday, or by streaming the event on Apple TV. Live streaming of the event on Apple's website requires a Safari browser on either the OSX or iOS operating systems.