The general consensus is that Apple will introduce new iPhones with larger screens in a few days. With many people with disabilities using Apple's flagship device for their accessibility needs a change can have a large impact on users. From a software prospective iOS 8 will offer many accessibility improvements, but hardware is also an important aspect of accessibility. The larger screen will certainly benefit some users with special needs, but may also cause problems for others.
Users with low vision may benefit the most from the larger viewing area. On current iPhones, with large text enabled, only a small amount of text is able to fit on screen. A larger screen will allow more text to fit on screen requiring less scrolling for users who prefer or require large text. The large screen will also give VoiceOver users more space to use three or four finger gestures.
On the other hand a larger screen iPhone may pose a challenge. Users with physical challenges may have a difficult time reaching all the controls. Also users who prefer using their phone in one hand and users who can only use one hand to operate their phone may find it difficult access all areas of the screen. It is possible that Apple will come up with a software solution to these possible challenges, making one handed use a breeze.
When Apple introduced the iPhone 5 it claimed that the larger screen was a perfect size for one handed, use so it will be interesting to see how the next iPhone is marketed.
People who use Apple devices as assistive devices should be excited about the company's upcoming announcement. Regardless of any hardware changes Apple's iOS 8 includes unmatched accessibility features for people with a variety of needs. The potentially larger screen size will likely benefit most users. The benefits and trade-offs of larger screen phones has been explored with Android phones for years, and hopefully Apple has been able to iron out any lasting challenges. Aside from the form factor, Apple may introduce new software or hardware features that impact people with disabilities at their event. Stay tuned for information about how Apple's announcements impact accessibility.