As excitement grows for the September 9 arrival of Apple's iPhone 6 and iOS 8, developers have expressed concerns over the new operating system.

The new class of apps will include more shared apps with heavy dependence on cloud APIs, and will be more networked with support for peripherals, like iWatch, HomeKit and HealthKit options.

There will also be more developer adoption of security conscious apps (with touch ID made available to more apps), and, generally, the apps will be richer – with more processing power, better graphics and full utilisation of the device size.

So what are the concerns? Here, Crittercism CEO Andrew Levy reveals the top five.

1. Increased customisation and flexibility

Apple’s iOS 8 has 4,000 new APIs to address new capabilities in the upcoming iPhone6 and OS. This large number means each of the new APIs needs to be thoroughly tested and validated.

However, not all app issues that will arise with the new device and OS will be caught in developers’ beta period. What’s more, these bugs may lead to unintended app performance and crashes for users.

2. Increased reliance on cloud connectivity

Many iOS features (like Handoff) rely on the ability to connect, network and sync with iCloud services. This means that for a seamless user experience, apps not only need to be free of crashes, but the cloud services they rely upon must also work correctly.

The more an app relies on these services, the higher the chances for additional performance issues.

3. Internet of Things support

Apple’s upcoming HealthKit and HomeKit will substantially increase the number of devices that the iPhone 6 and iOS8 will connect to. Anytime you increase the number of devices, you run the risk of potential errors.

Also, the proliferation of HealthKit and HomeKit will spur a wave of third-party apps and developers (as well as Apple) that will need to be ready to create seamless communication with these apps.

4. New device support

The announcement of the iPhone 6 (along with its subsystem) with the new OS will add to the complexity of the app ecosystem.

With this, app developers will have to race to release apps that fully take advantage of the capabilities of the new OS as well as the device.

5. New swift programming language

Apple’s new programming language for Cocoa and Cocoa Touch, Swift, will come out with the iOS 8. This, just as any new language, will introduce complexities that developers will have to learn and adapt to.

Developers should familiarise themselves with any and all details currently available on the language to get a jump on the competition.